D7464: filemerge: drop a default argument to appease pytype

[mharbison72 (Matt Harbison)]

mharbison72 added a comment.


  In D7464#109795 <https://phab.mercurial-scm.org/D7464#109795>, @dlax wrote:
  
  > Shouldn't this be also done for all similar functions? (i.e. `_xmergeimm` and functions registered as a merge tool with `@internaltool`)
  
  I looked at this  a bit more, and it looks like the other functions either ignore the `labels` arg, or they handle the `None`/empty case to substitute something else.  So maybe that's a better thing to do.  But I'm not real familiar with merge code, and don't know what the default labels should be here.

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