[PATCH 1 of 4] merge: drop special parent assignment in the obsolete case

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1444034853 25200
#      Mon Oct 05 01:47:33 2015 -0700
# Node ID 23de95a90992c0bd0ea76b17e6c9ba2fba5f3c13
# Parent  f71ff13ffcc99ca3f4851de1e1cebbdb4b3de913
merge: drop special parent assignment in the obsolete case

We can safely drop this because the very same assignment is enforcement later in
the function. Dropping it will make it simpler to extract the default
destination logic in its own function.

diff --git a/mercurial/merge.py b/mercurial/merge.py
--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -995,12 +995,10 @@ def update(repo, node, branchmerge, forc
 
         if node is None:
             nodes = list(repo.set('_updatedefaultdest()'))
             if nodes:
                 node = nodes[0].node()
-                if p1.obsolete() and not p1.children():
-                    pas = [p1]
 
         overwrite = force and not branchmerge
 
         p2 = repo[node]
         if pas[0] is None: