remove non-prefixed environment variables from hooks.

doc/hgrc.5.txt

@@ -234,10 +234,9 b' hooks::'
     is in $HG_PARENT2.  If update succeeded, $HG_ERROR=0.  If update
     failed (e.g. because conflicts not resolved), $HG_ERROR=1.
 
-  In earlier releases, the names of hook environment variables did not
-  have a "HG_" prefix.  These unprefixed names are still provided in
-  the environment for backwards compatibility, but their use is
-  deprecated, and they will be removed in a future release.
+  Note: In earlier releases, the names of hook environment variables
+  did not have a "HG_" prefix.  The old unprefixed names are no longer
+  provided in the environment.
 
   The syntax for Python hooks is as follows:
 

mercurial/localrepo.py

@@ -136,8 +136,7 b' class localrepository(object):'
 
         def runhook(name, cmd):
             self.ui.note(_("running hook %s: %s\n") % (name, cmd))
-            env = dict([('HG_' + k.upper(), v) for k, v in args.iteritems()] +
-                       [(k.upper(), v) for k, v in args.iteritems()])
+            env = dict([('HG_' + k.upper(), v) for k, v in args.iteritems()])
             r = util.system(cmd, environ=env, cwd=self.root)
             if r:
                 desc, r = util.explain_exit(r)