Issue #2127941 by Gábor Hojtsy: Remove two (out of 3) bogus and duplicate date languages UIs.

core/modules/language/language.local_tasks.yml

...e/tests/Drupal/language/Tests/Menu/LanguageLocalTasks.php

core/modules/system/config/schema/system.schema.yml

core/modules/system/config/system.date_format.fallback.yml

core/modules/system/config/system.date_format.html_date.yml

...odules/system/config/system.date_format.html_datetime.yml

core/modules/system/config/system.date_format.html_month.yml

core/modules/system/config/system.date_format.html_time.yml

core/modules/system/config/system.date_format.html_week.yml

core/modules/system/config/system.date_format.html_year.yml

...s/system/config/system.date_format.html_yearless_date.yml

core/modules/system/config/system.date_format.long.yml

core/modules/system/config/system.date_format.medium.yml

core/modules/system/config/system.date_format.short.yml

...Drupal/system/Controller/DateFormatLanguageController.php

.../modules/system/lib/Drupal/system/DateFormatInterface.php

core/modules/system/lib/Drupal/system/Entity/DateFormat.php

...ules/system/lib/Drupal/system/Form/DateFormatFormBase.php

...em/lib/Drupal/system/Form/DateFormatLocalizeResetForm.php

core/modules/system/lib/Drupal/system/Form/SystemForm.php