Five methods in class TestFormBuilder are dead code. Remove them.

There are four utility methods in class TestFormBuilder that seem to never be used:

drupal8x (isssue/static)$ grep -r "drupalHtmlClass(" core/
core//tests/Drupal/Tests/Core/Form/FormTestBase.php:  protected function drupalHtmlClass($class) {
drupal8x (isssue/static)$ grep -r "drupalHtmlId(" core/
core//tests/Drupal/Tests/Core/Form/FormTestBase.php:  protected function drupalHtmlId($id) {
drupal8x (isssue/static)$ grep -r "drupalStaticReset(" core/
core//tests/Drupal/Tests/Core/Form/FormTestBase.php:  public function drupalStaticReset($name = NULL) {
drupal8x (isssue/static)$ grep -r "requestUri(" core/
core//tests/Drupal/Tests/Core/Form/FormTestBase.php:  protected function requestUri() {

Also ::sendResponse() is never called. There is a test method in FormBuilderTest that claims to test it but it never calls ::sendResponse() nor does it make any asserts.

They can probably all be removed.