pgsql: Remove useless "rough estimate" path from mcelem_array_contained

Remove useless "rough estimate" path from mcelem_array_contained_selec.

The code in this function that tried to cope with a missing count histogram
was quite ineffective for anything except a perfectly flat distribution.
Furthermore, since we were already punting for missing MCELEM slot, it's
rather useless to sweat over missing DECHIST: there are no cases where
ANALYZE will create the first but not the second.  So just simplify the
code by punting rather than pretending we can do something useful.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/e2eed7891008cbf2b7d3868b3d77751b33ed09ad

Modified Files
--------------
src/backend/utils/adt/array_selfuncs.c |  138 ++++++++++++++-----------------
1 files changed, 62 insertions(+), 76 deletions(-)