changegroup: stop treating strip as special when dealing with phases

Since 8e3021fd1a44, the strip bundle includes the phases of the stripping
node. Hence we don't need this special case anymore.

Dropping it will helps make the phase behavior more consistent across all
exchanges medium.

mercurial/changegroup.py

@@ -372,10 +372,7 b' class cg1unpacker(object):'
                     # ignored.
                     phases.advanceboundary(repo, tr, phases.draft, cgnodes)
                     phases.retractboundary(repo, tr, phases.draft, added)
-            elif srctype != 'strip':
-                # publishing only alter behavior during push
-                #
-                # strip should not touch boundary at all
+            else:
                 phases.retractboundary(repo, tr, targetphase, added)
 
             if changesets > 0: