copies: remove msrc and mdst parameters

This function already has lots of parameters. And we can get manifests from
contexts. So let's get msrc and mdst parameters from srcctx and dstctx.

mercurial/copies.py

@@ -414,10 +414,10 b' def mergecopies(repo, c1, c2, base):'
                                       baselabel='topological common ancestor')
 
     for f in u1u:
-        _checkcopies(c1, c2, f, m1, m2, base, tca, dirtyc1, limit, data1)
+        _checkcopies(c1, c2, f, base, tca, dirtyc1, limit, data1)
 
     for f in u2u:
-        _checkcopies(c2, c1, f, m2, m1, base, tca, dirtyc2, limit, data2)
+        _checkcopies(c2, c1, f, base, tca, dirtyc2, limit, data2)
 
     copy = dict(data1['copy'].items() + data2['copy'].items())
     fullcopy = dict(data1['fullcopy'].items() + data2['fullcopy'].items())
@@ -462,8 +462,8 b' def mergecopies(repo, c1, c2, base):'
              'incompletediverge': bothincompletediverge
             }
     for f in bothnew:
-        _checkcopies(c1, c2, f, m1, m2, base, tca, dirtyc1, limit, both1)
-        _checkcopies(c2, c1, f, m2, m1, base, tca, dirtyc2, limit, both2)
+        _checkcopies(c1, c2, f, base, tca, dirtyc1, limit, both1)
+        _checkcopies(c2, c1, f, base, tca, dirtyc2, limit, both2)
     if dirtyc1:
         # incomplete copies may only be found on the "dirty" side for bothnew
         assert not both2['incomplete']
@@ -598,16 +598,13 b' def _related(f1, f2, limit):'
     except StopIteration:
         return False
 
-def _checkcopies(srcctx, dstctx, f, msrc, mdst, base, tca, remotebase,
-                 limit, data):
+def _checkcopies(srcctx, dstctx, f, base, tca, remotebase, limit, data):
     """
     check possible copies of f from msrc to mdst
 
     srcctx = starting context for f in msrc
     dstctx = destination context for f in mdst
     f = the filename to check (as in msrc)
-    msrc = the source manifest
-    mdst = the destination manifest
     base = the changectx used as a merge base
     tca = topological common ancestor for graft-like scenarios
     remotebase = True if base is outside tca::srcctx, False otherwise
@@ -620,6 +617,8 b' def _checkcopies(srcctx, dstctx, f, msrc'
     once it "goes behind a certain revision".
     """
 
+    msrc = srcctx.manifest()
+    mdst = dstctx.manifest()
     mb = base.manifest()
     mta = tca.manifest()
     # Might be true if this call is about finding backward renames,