Issue #3097173 by alexpott, Berdir: Complete removal of $config_directories

core/globals.api.php

core/includes/install.core.inc

core/lib/Drupal/Core/DrupalKernel.php

core/lib/Drupal/Core/Site/Settings.php

core/lib/Drupal/Core/Test/FunctionalTestSetupTrait.php

core/modules/simpletest/src/TestBase.php

core/modules/system/system.install

...modules/system/tests/src/Functional/System/StatusTest.php

...aller/InstallerConfigDirectorySetNoDirectoryErrorTest.php

...lTests/Installer/InstallerExistingConfigDirectoryTest.php

...Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php

core/tests/Drupal/Tests/Core/Site/SettingsTest.php