trydiff: remove unused variable 'modifiedset'

We started updating 'modifiedset' in a9853fc172d2 (trydiff: simplify
checking for additions, 2014-12-23) but in the same commit, we removed
the last use of the variable. Clean it up.

mercurial/patch.py

@@ -1788,13 +1788,12 b' def trydiff(repo, revs, ctx1, ctx2, modi'
     if opts.git:
         revs = None
 
-    modifiedset, addedset, removedset = set(modified), set(added), set(removed)
-    # Fix up modified and added, since merged-in additions appear as
+    addedset, removedset = set(added), set(removed)
+    # Fix up  added, since merged-in additions appear as
     # modifications during merges
-    for f in modifiedset.copy():
+    for f in modified:
         if f not in ctx1:
             addedset.add(f)
-            modifiedset.remove(f)
     for f in sorted(modified + added + removed):
         to = None
         tn = None