6 files declare their use of LocalTaskDefault in Drupal 8

ConfigTranslationLocalTask.php in core/modules/config_translation/src/Plugin/Menu/LocalTask/ConfigTranslationLocalTask.php

LocalTaskDefaultTest.php in core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php

Contains \Drupal\Tests\Core\Menu\LocalTaskDefaultTest.

TestTasksSettingsSub1.php in core/modules/system/tests/modules/menu_test/src/Plugin/Menu/LocalTask/TestTasksSettingsSub1.php

TestTaskWithUserInput.php in core/modules/system/tests/modules/menu_test/src/Plugin/Menu/LocalTask/TestTaskWithUserInput.php

UnapprovedComments.php in core/modules/comment/src/Plugin/Menu/LocalTask/UnapprovedComments.php

UserTrackerTab.php in core/modules/tracker/src/Plugin/Menu/UserTrackerTab.php