changegroup: deduplicate 'getlocalchangegroup'

changegroup: deduplicate 'getlocalchangegroup'

The two functions 'getlocalchangegroup' and 'getchangegroup' have been strictly
identical for multiple years ('getchangegroup' had a deprecated docstring)

We'll drop one of them (getlocalchangegroup, since it has the longest name).
However, we needs to migrate all users of the dropped one to the new one before
we can deprecate it. In the mean time we drop one of the duplicated definition
and the outdated docstring.

--- a/mercurial/changegroup.py	Thu May 04 04:57:30 2017 +0530
+++ b/mercurial/changegroup.py	Thu May 04 12:36:45 2017 +0200
@@ -966,7 +966,7 @@
     bundler = getbundler(version, repo)
     return getsubsetraw(repo, outgoing, bundler, source)
 
-def getlocalchangegroup(repo, source, outgoing, version='01'):
+def getchangegroup(repo, source, outgoing, version='01'):
     """Like getbundle, but taking a discovery.outgoing as an argument.
 
     This is only implemented for local repos and reuses potentially
@@ -976,16 +976,8 @@
     bundler = getbundler(version, repo)
     return getsubset(repo, outgoing, bundler, source)
 
-def getchangegroup(repo, source, outgoing, version='01'):
-    """Like changegroupsubset, but returns the set difference between the
-    ancestors of heads and the ancestors common.
-
-    If heads is None, use the local heads. If common is None, use [nullid].
-
-    The nodes in common might not all be known locally due to the way the
-    current discovery protocol works.
-    """
-    return getlocalchangegroup(repo, source, outgoing, version=version)
+# deprecate me once all users are gone
+getlocalchangegroup = getchangegroup
 
 def changegroup(repo, basenodes, source):
     # to avoid a race we use changegroupsubset() (issue1320)