When reassigning a proof and changing owner, allow the proof creator to be removed from proof.

Description -

Why is this feature important to you -  We are constantly moving projects around and have PM's cover for each other while on vacation and getting the proof set back to the correct owner and to have the PM that set up proof continue to receive notifications on something that they are no longer responsible for would be great. 

How would you like the feature to work - Allow the proof creator to be removed from a proof after ownership has been transfer

Current Behaviour - Cannot remove a proof creator from a proof