remove duplicated method from moves_controller

The find_work_package method was present in
work_packages/moves_controller.rb as well as in
application_controller.rb.

As the MovesController inherits from Application controller and the
methods in both controllers are identical, it can be removed from the
MovesController.

see: https://codeclimate.com/repos/528f351813d637200e02ef84/WorkPackages::MovesController