D857: py3: add a test showing a normal `hg merge` works on Python 3

[pulkit (Pulkit Goyal)]

pulkit added a comment.


  In https://phab.mercurial-scm.org/D857#14374, @durin42 wrote:
  
  > Do we need this with https://phab.mercurial-scm.org/D858? It looks like we get enough extra coverage from that we don't need this extra check here.
  
  
  Yeah I guess we don't even need that file now. But I will leave that for now as it is.

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D857

To: pulkit, #hg-reviewers
Cc: durin42, mercurial-devel