Fixed set_process_input on free_look_camera scripts preventing cameras from being reactivated.

The use of set_process and set_process_input on the activate/deactivate methods of the free_look_camera scripts were preventing cameras from being reactivated after being deactivated once, since they stopped listening for input. The _input function already checks if the camera is active before processing any movement, so removing the calls to set_process gets them working correctly.

This also fixes a typo on free_look_camera_2d.gd that calls for Vector2.DOWN on move_up_key and vice versa.