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
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/0aff9d8338d6fa6b9ef2439c7c0b4aa3ad4a4651

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