merge: remove last traces of fastforward merging

bbc97d419b16 introduced fast-forward branch merging.
66ed92ed115a partly removed it again.

The fastforward variable would always be false if branchmerge was false, so the
fastforward variable makes no difference and we can remove it completely.

mercurial/merge.py

@@ -493,7 +493,6 b' def update(repo, node, branchmerge, forc'
         p1, p2 = pl[0], repo[node]
         pa = p1.ancestor(p2)
         fp1, fp2, xp1, xp2 = p1.node(), p2.node(), str(p1), str(p2)
-        fastforward = False
 
         ### check phase
         if not overwrite and len(pl) > 1:
@@ -503,9 +502,7 b' def update(repo, node, branchmerge, forc'
                 raise util.Abort(_("merging with a working directory ancestor"
                                    " has no effect"))
             elif pa == p1:
-                if p1.branch() != p2.branch():
-                    fastforward = True
-                else:
+                if p1.branch() == p2.branch():
                     raise util.Abort(_("nothing to merge (use 'hg update'"
                                        " or check 'hg heads')"))
             if not force and (wc.files() or wc.deleted()):
@@ -550,7 +547,7 b' def update(repo, node, branchmerge, forc'
         if not partial:
             repo.dirstate.setparents(fp1, fp2)
             recordupdates(repo, action, branchmerge)
-            if not branchmerge and not fastforward:
+            if not branchmerge:
                 repo.dirstate.setbranch(p2.branch())
     finally:
         wlock.release()