copies: delete misplaced comment

The comment was added in 78d760aa3607 (duplicatecopies: do not mark
items not in the dirstate as copies, 2013-03-28). It became misplaced
in 3666331164bb (cmdutil: add copy-filtering support to
duplicatecopies, 2014-06-07). Then the relevant code was moved far
away in 754b5117622f (context: add workingfilectx.markcopied,
2017-10-15).

Differential Revision: https://phab.mercurial-scm.org/D6352

mercurial/copies.py

@@ -796,8 +796,6 b' def duplicatecopies(repo, wctx, rev, fro'
         # metadata across the rebase anyway).
         exclude = pathcopies(repo[fromrev], repo[skiprev])
     for dst, src in pathcopies(repo[fromrev], repo[rev]).iteritems():
-        # copies.pathcopies returns backward renames, so dst might not
-        # actually be in the dirstate
         if dst in exclude:
             continue
         wctx[dst].markcopied(src)