Issue #2209337 by tstoeckler: Remove hidden property from test extensions.

core/modules/config/tests/config_test/config_test.info.yml

core/modules/config/tests/config_test_invalid_name/install

.../config_translation_test/config_translation_test.info.yml

...slation_test_theme/config_translation_test_theme.info.yml

...ts/modules/contact_test_views/contact_test_views.info.yml

...lation_test_views/content_translation_test_views.info.yml

.../tests/modules/dblog_test_views/dblog_test_views.info.yml

core/modules/editor/tests/modules/editor_test.info.yml

...ules/entity_reference_test/entity_reference_test.info.yml

...odules/field/tests/modules/field_test/field_test.info.yml

...ests/modules/field_test_config/field_test_config.info.yml

.../tests/modules/field_test_views/field_test_views.info.yml

...eld_ui/tests/modules/field_ui_test/field_ui_test.info.yml

...les/file/tests/file_module_test/file_module_test.info.yml

core/modules/file/tests/file_test/file_test.info.yml

...le/tests/modules/file_test_views/file_test_views.info.yml

core/modules/filter/tests/filter_test/filter_test.info.yml

.../tests/modules/forum_test_views/forum_test_views.info.yml

...ests/modules/image_module_test/image_module_test.info.yml

...ts/language_elements_test/language_elements_test.info.yml