diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index c9ad780..a875b89 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -117,41 +117,6 @@
  */
 
 /**
- * First bootstrap phase: initialize configuration.
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- */
-const DRUPAL_BOOTSTRAP_CONFIGURATION = 0;
-
-/**
- * Second bootstrap phase, initialize a kernel.
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- */
-const DRUPAL_BOOTSTRAP_KERNEL = 1;
-
-/**
- * Third bootstrap phase: try to serve a cached page.
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- */
-const DRUPAL_BOOTSTRAP_PAGE_CACHE = 2;
-
-/**
- * Fourth bootstrap phase: load code for subsystems and modules.
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- */
-const DRUPAL_BOOTSTRAP_CODE = 3;
-
-/**
- * Final bootstrap phase: initialize language, path, theme, and modules.
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- */
-const DRUPAL_BOOTSTRAP_FULL = 4;
-
-/**
  * Role ID for anonymous users; should match what's in the "role" table.
  */
 const DRUPAL_ANONYMOUS_RID = 'anonymous';
@@ -968,63 +933,6 @@ function drupal_get_messages($type = NULL, $clear_queue = TRUE) {
 }
 
 /**
- * Ensures Drupal is bootstrapped to the specified phase.
- *
- * In order to bootstrap Drupal from another PHP script, you can use this code:
- * @code
- *   require_once '/path/to/drupal/core/vendor/autoload.php';
- *   require_once '/path/to/drupal/core/includes/bootstrap.inc';
- *   drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
- * @endcode
- *
- * @param $phase
- *   A constant telling which phase to bootstrap to. Possible values:
- *   - DRUPAL_BOOTSTRAP_CONFIGURATION: Initializes configuration.
- *   - DRUPAL_BOOTSTRAP_KERNEL: Initializes a kernel.
- *
- * @return int
- *   The most recently completed phase.
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- *   Interact directly with the kernel.
- */
-function drupal_bootstrap($phase = NULL) {
-  // Temporary variables used for booting later legacy phases.
-  /** @var \Drupal\Core\DrupalKernel $kernel */
-  static $kernel;
-  static $boot_level = 0;
-
-  if (isset($phase)) {
-    $request = Request::createFromGlobals();
-    for ($current_phase = $boot_level; $current_phase <= $phase; $current_phase++) {
-
-      switch ($current_phase) {
-        case DRUPAL_BOOTSTRAP_CONFIGURATION:
-          $classloader = require __DIR__ . '/../vendor/autoload.php';
-          $kernel = DrupalKernel::createFromRequest($request, $classloader, 'prod');
-          break;
-
-        case DRUPAL_BOOTSTRAP_KERNEL:
-          $kernel->boot();
-          break;
-
-        case DRUPAL_BOOTSTRAP_PAGE_CACHE:
-          $kernel->handlePageCache($request);
-          break;
-
-        case DRUPAL_BOOTSTRAP_CODE:
-        case DRUPAL_BOOTSTRAP_FULL:
-          $kernel->prepareLegacyRequest($request);
-          break;
-      }
-    }
-    $boot_level = $phase;
-  }
-
-  return \Drupal::getContainer() ? DRUPAL_BOOTSTRAP_CODE : DRUPAL_BOOTSTRAP_CONFIGURATION;
-}
-
-/**
  * Returns the time zone of the current user.
  */
 function drupal_get_user_timezone() {
@@ -1091,19 +999,6 @@ function _drupal_exception_handler($exception) {
 }
 
 /**
- * Returns the current bootstrap phase for this Drupal process.
- *
- * The current phase is the one most recently completed by drupal_bootstrap().
- *
- * @see drupal_bootstrap()
- *
- * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
- */
-function drupal_get_bootstrap_phase() {
-  return drupal_bootstrap();
-}
-
-/**
  * Returns the list of enabled modules.
  *
  * @deprecated in Drupal 8.x-dev, will be removed before Drupal 8.0.
diff --git a/core/includes/errors.inc b/core/includes/errors.inc
index a0fe0c1..9f46946 100644
--- a/core/includes/errors.inc
+++ b/core/includes/errors.inc
@@ -121,7 +121,7 @@ function _drupal_log_error($error, $fatal = FALSE) {
   // Initialize a maintenance theme if the bootstrap was not complete.
   // Do it early because drupal_set_message() triggers a
   // \Drupal\Core\Theme\ThemeManager::initTheme().
-  if ($fatal && drupal_get_bootstrap_phase() < DRUPAL_BOOTSTRAP_CODE) {
+  if ($fatal && \Drupal::hasService('theme.manager')) {
     // The installer initializes a maintenance theme at the earliest possible
     // point in time already. Do not unset that.
     if (!$is_installer) {
@@ -250,8 +250,8 @@ function _drupal_log_error($error, $fatal = FALSE) {
 /**
  * Returns the current error level.
  *
- * This function should only be used to get the current error level prior to
- * DRUPAL_BOOTSTRAP_KERNEL or before Drupal is installed. In all other situations
+ * This function should only be used to get the current error level prior to the
+ * kernel being booted or before Drupal is installed. In all other situations
  * the following code is preferred:
  * @code
  * \Drupal::config('system.logging')->get('error_level');
diff --git a/core/includes/utility.inc b/core/includes/utility.inc
index ec6a20c..f0da4f3 100644
--- a/core/includes/utility.inc
+++ b/core/includes/utility.inc
@@ -33,8 +33,6 @@ function drupal_var_export($var, $prefix = '') {
 /**
  * Rebuilds all caches even when Drupal itself does not work.
  *
- * Requires DRUPAL_BOOTSTRAP_CONFIGURATION.
- *
  * @param \Composer\Autoload\ClassLoader $classloader
  *   The classloader.
  * @param \Symfony\Component\HttpFoundation\Request $request
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 3c826bf..5e1ca1b 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -822,8 +822,8 @@ protected function setUp() {
     }
 
     // Since Drupal is bootstrapped already, install_begin_request() will not
-    // bootstrap into DRUPAL_BOOTSTRAP_CONFIGURATION (again). Hence, we have to
-    // reload the newly written custom settings.php manually.
+    // bootstrap again. Hence, we have to reload the newly written custom
+    // settings.php manually.
     $class_loader = require DRUPAL_ROOT . '/core/vendor/autoload.php';
     Settings::initialize($directory, $class_loader);
 
