pgsql: Remove unnecessary variables in _hash_splitbucket().

Remove unnecessary variables in _hash_splitbucket().

Commit ed9cc2b5df59fdbc50cce37399e26b03ab2c1686 made it unnecessary to pass
start_nblkno to _hash_splitbucket(), and for that matter unnecessary to
have the internal nblkno variable either. My compiler didn't complain
about that, but some did. I also rearranged the use of oblkno a bit to
make that case more parallel.

Report and initial patch by Petr Jelinek, rearranged a bit by me.
Back-patch to all branches, like the previous patch.

Branch
------
REL9_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/645081427d52bdfa88b79d886df2cbab5c72d406

Modified Files
--------------
src/backend/access/hash/hashpage.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)