Issue #3269143 by longwave, catch: Remove deprecated theme key stylesheets-remove

core/lib/Drupal/Core/Asset/AssetResolver.php

core/lib/Drupal/Core/Theme/ActiveTheme.php

core/lib/Drupal/Core/Theme/ThemeInitialization.php

...es/system/tests/modules/theme_test/theme_test.routing.yml

...ests/src/Functional/Theme/LegacyStyleSheetsRemoveTest.php

...dules/system/tests/src/Functional/Theme/ThemeInfoTest.php

...tylesheets_remove/test_legacy_stylesheets_remove.info.yml

core/tests/Drupal/Tests/Core/Theme/RegistryTest.php