Issue #2301319 by pwolanin, effulgentsia: MenuLinkNG part5: Remove dead code and party!

core/includes/menu.inc

core/modules/menu_link/menu_link.api.php

core/modules/menu_link/menu_link.install

core/modules/menu_link/menu_link.module

core/modules/menu_link/menu_link.services.yml

core/modules/menu_link/src/Entity/MenuLink.php

core/modules/menu_link/src/MenuLinkAccessController.php

core/modules/menu_link/src/MenuLinkForm.php

core/modules/menu_link/src/MenuLinkInterface.php

core/modules/menu_link/src/MenuLinkStorage.php

core/modules/menu_link/src/MenuLinkStorageInterface.php

core/modules/menu_link/src/MenuTree.php

core/modules/menu_link/src/MenuTreeInterface.php

core/modules/menu_link/src/StaticMenuLinks.php

core/modules/menu_link/tests/src/MenuTreeTest.php

core/modules/views/src/Plugin/views/sort/MenuHierarchy.php