That tab is there to make sure you plug it in with the correct polarity. Now that its gone you can plug it in backwards and possibly fry the servo - the black wire goes to the outside of the rx. Or, the side where the tab used to be goes to the inside.

I cut them off too to use in other rxs, just have to be a little careful to make sure you're getting polarity right. Seen folks get in a hurry, forget what they've done and mess up a good servo.