Issue #2084197 by tim.plunkett: Fixed Uninstalling menu module removes all custom menus.

core/modules/block/block.api.php

core/modules/block/block.module

.../modules/block/lib/Drupal/block/Tests/BlockHtmlIdTest.php

...b/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php

core/modules/block/lib/Drupal/block/Tests/BlockUiTest.php

core/modules/menu/lib/Drupal/menu/Form/MenuDeleteForm.php

core/modules/menu/lib/Drupal/menu/MenuFormController.php

core/modules/menu/lib/Drupal/menu/Plugin/Block/MenuBlock.php

...ules/menu/lib/Drupal/menu/Plugin/Derivative/MenuBlock.php

core/modules/menu/lib/Drupal/menu/Tests/MenuLanguageTest.php

core/modules/menu/lib/Drupal/menu/Tests/MenuTest.php

.../modules/menu/lib/Drupal/menu/Tests/MenuUninstallTest.php

core/modules/menu/menu.install

core/modules/menu/menu.module

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

core/modules/system/config/system.menu.account.yml

core/modules/system/config/system.menu.admin.yml

core/modules/system/config/system.menu.footer.yml

core/modules/system/config/system.menu.main.yml

core/modules/system/config/system.menu.tools.yml