D7464: filemerge: drop a default argument to appease pytype

[dlax (Denis Laxalde)]

dlax added a comment.


  Shouldn't this be also done for all similar functions? (i.e. `_xmergeimm` and functions registered as a merge tool with `@internaltool`)

REPOSITORY
  rHG Mercurial

CHANGES SINCE LAST ACTION
  https://phab.mercurial-scm.org/D7464/new/

REVISION DETAIL
  https://phab.mercurial-scm.org/D7464

To: mharbison72, #hg-reviewers
Cc: dlax, mercurial-devel