Load sensing proportioning valve. It is a lever that opens a valve to allow more fluid to the rear brakes when the suspension is compressed, providing better braking with a heavy load.
You may be able to make a bracket to lift the arm back to the stock position. Or just delete it, block the T-fitting in the front that leads to it, and install a manual proportioning valve.
The simplest thing is to disconnect it at the axle and tie the rod up to the frame.
That gives you max power to the rear brakes and the least amount of work.