Simpletest cleanup-related functions replaced, deprecated

In order to further isolate the simpletest module from core's test runner infrastructure, simpletest_clean_*() functions have been moved to some environmental cleaner classes.

These functions have been deprecated:

• simpletest_clean_environment()
• simpletest_clean_database()
• simpletest_clean_temporary_directories()
• simpletest_clean_results_table()

These have been replaced by classes which implement the Drupal\Core\Test\EnvironmentCleanerInterface interface:

• Drupal\Core\Test\EnvironmentCleanerInterface::cleanEnvironment($clear_results = TRUE, $clear_temp_directories = TRUE, $clear_database = TRUE)
• Drupal\Core\Test\EnvironmentCleanerInterface::cleanDatabase()
• Drupal\Core\Test\EnvironmentCleanerInterface::cleanTemporaryDirectories()
• Drupal\Core\Test\EnvironmentCleanerInterface::cleanResultsTable($test_id = NULL)

Within the simpletest module, developers should access the environment_cleaner service and call the desired method.

In other contexts, developers should create a new Drupal\Core\Test\EnvironmentCleaner object and use it to clean up after tests.