D821: unamend: move fb extension unamend to core

[pulkit (Pulkit Goyal)]

pulkit planned changes to this revision.
pulkit added a comment.


  In https://phab.mercurial-scm.org/D821#14116, @singhsrb wrote:
  
  > I just wanted to mention that unamend command does not track copytrace information properly.
  
  
  That's a pretty good catch. Thanks a lot.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D821

To: pulkit, #hg-reviewers, durham
Cc: singhsrb, durham, mercurial-devel