Remove simpleSelectManagement and simpleManagement
Now that the last plugins got migrated to selectManagement (See fd-plugins#6006 (closed) and fd-plugins#6007 (closed)), these classes and associated code can be removed from core.
Now that the last plugins got migrated to selectManagement (See fd-plugins#6006 (closed) and fd-plugins#6007 (closed)), these classes and associated code can be removed from core.