Issue #3110137 by bnjmnm, Spokje, lauriii, Mixologic: Remove Classy from core

core/MAINTAINERS.txt

core/misc/cspell/dictionary.txt

...modules/help_topics/help_topics/core.appearance.html.twig

core/modules/media/templates/media-reference-help.html.twig

core/modules/settings_tray/settings_tray.libraries.yml

core/profiles/demo_umami/themes/umami/README.txt

core/profiles/demo_umami/themes/umami/css/classy/README.txt

...mo_umami/themes/umami/css/classy/components/ui-dialog.css

...s/demo_umami/themes/umami/css/components/fields/field.css

...profiles/demo_umami/themes/umami/images/classy/README.txt

core/profiles/demo_umami/themes/umami/js/classy/README.txt

...mami/themes/umami/js/classy/media_embed_ckeditor.theme.js

...files/demo_umami/themes/umami/templates/classy/README.txt

.../classy/media-library/links--media-library-menu.html.twig

core/profiles/demo_umami/themes/umami/umami.theme

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

...Drupal/Tests/Core/Theme/ClassyPreprocessUnchangedTest.php

...Tests/Core/Theme/ClassyTemplatesIdenticalToStableTest.php

core/themes/claro/claro.theme

core/themes/claro/css/classy/README.txt