remove obsolete code from patch.diff

repo.status already does this filtering.  If the caller supplies a set of
changes, it's his responsibility to filter out what he doesn't want.

mercurial/patch.py

@@ -466,17 +466,6 b' def diff(repo, node1=None, node2=None, f'
     if not changes:
         changes = repo.status(node1, node2, files, match=match)[:5]
     modified, added, removed, deleted, unknown = changes
-    if files:
-        def filterfiles(filters):
-            l = [x for x in filters if x in files]
-
-            for t in files:
-                if not t.endswith("/"):
-                    t += "/"
-                l += [x for x in filters if x.startswith(t)]
-            return l
-
-        modified, added, removed = map(filterfiles, (modified, added, removed))
 
     if not modified and not added and not removed:
         return