I looked up the Grayson Hobby Advanced Edition 50a ESC and that is an OPTO type with no built in battery eliminator circuit.
The device you cut off is the BEC (battery eliminator circuit) and it provides 5 or 6 volts DC (depending how the jumper is set) to the receiver.
You need to connect it back to the battery plug lead and then connect the Futaba servo plug into the receivers battery port or any spare port.
Then when you connect the lipo up the receiver now will have power and you can bind it to your transmitter.