remote-hg: simplify branch_tip()

It simply picks the last head that is not closed, but we have a stored
list of open heads.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/remote-helpers/git-remote-hg

@@ -560,12 +560,8 @@ def do_capabilities(parser):
 
     print
 
-def branch_tip(repo, branch):
-    # older versions of mercurial don't have this
-    if hasattr(repo, 'branchtip'):
-        return repo.branchtip(branch)
-    else:
-        return repo.branchtags()[branch]
+def branch_tip(branch):
+    return branches[branch][-1]
 
 def get_branch_tip(repo, branch):
     global branches
@@ -577,7 +573,7 @@ def get_branch_tip(repo, branch):
     # verify there's only one head
     if (len(heads) > 1):
         warn("Branch '%s' has more than one head, consider merging" % branch)
-        return branch_tip(repo, hgref(branch))
+        return branch_tip(hgref(branch))
 
     return heads[0]
 
@@ -828,7 +824,7 @@ def parse_tag(parser):
 
 def write_tag(repo, tag, node, msg, author):
     branch = repo[node].branch()
-    tip = branch_tip(repo, branch)
+    tip = branch_tip(branch)
     tip = repo[tip]
 
     def getfilectx(repo, memctx, f):