copies: remove dependency on scmutil by directly using match.exact()

I want to add a dependency from scmutil.copies(), so I need to remove
this dependency first.

Differential Revision: https://phab.mercurial-scm.org/D6118

mercurial/copies.py

@@ -17,7 +17,6 b' from . import ('
     match as matchmod,
     node,
     pathutil,
-    scmutil,
     util,
 )
 from .utils import (
@@ -193,7 +192,7 b' def _committedforwardcopies(a, b, match)'
     # this comparison.
     forwardmissingmatch = match
     if b.p1() == a and b.p2().node() == node.nullid:
-        filesmatcher = scmutil.matchfiles(a._repo, b.files())
+        filesmatcher = matchmod.exact(b.files())
         forwardmissingmatch = matchmod.intersectmatchers(match, filesmatcher)
     missing = _computeforwardmissing(a, b, match=forwardmissingmatch)