Issue #3115088 by lauriii, bnjmnm, tim.plunkett: Remove Classy as a base theme of core themes

...ules/block_test/config/install/block.block.test_block.yml

core/modules/ckeditor/tests/src/Kernel/CKEditorTest.php

...odules/config/tests/src/Functional/ConfigImportUITest.php

core/modules/system/system.post_update.php

...tests/src/Functional/Update/ClassyUninstallUpdateTest.php

.../Functional/UpdateSystem/UpdatePathTestBaseFilledTest.php

...umami/themes/umami/css/classy/components/image-widget.css

core/profiles/demo_umami/themes/umami/umami.info.yml

core/profiles/demo_umami/themes/umami/umami.libraries.yml

...sts/Drupal/KernelTests/Core/Config/ConfigImporterTest.php

...Drupal/KernelTests/Core/Theme/ConfirmClassyCopiesTest.php

...ts/Drupal/KernelTests/Core/Theme/MaintenanceThemeTest.php

...KernelTests/Core/Theme/ThemeNotUsingClassyLibraryTest.php

...nelTests/Core/Theme/ThemesNotUsingClassyTemplatesTest.php

core/themes/bartik/bartik.info.yml

core/themes/bartik/bartik.libraries.yml

core/themes/bartik/css/classy/components/image-widget.css

core/themes/bartik/css/classy/components/indented.css

core/themes/claro/claro.info.yml

core/themes/claro/claro.libraries.yml