pgsql: Use ExecPrepareExpr in place of ExecPrepareCheck where appropria

Use ExecPrepareExpr in place of ExecPrepareCheck where appropriate.

Change one more place where ExecInitCheck/ExecPrepareCheck's insistence
on getting implicit-AND-format quals wasn't really helpful, because the
caller had to do make_ands_implicit() for no reason that it cared about.
Using ExecPrepareExpr directly simplifies the code and saves cycles.

The only remaining use of these functions is to process
resultRelInfo->ri_PartitionCheck quals. However, implicit-AND format
does seem to be what we want for that, so leave it alone.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9b95f2fa1e2684fa209a3594db2254b8841bf380

Modified Files
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src/backend/catalog/partition.c | 6 +++++-
src/backend/commands/tablecmds.c | 22 ++++++++++------------
2 files changed, 15 insertions(+), 13 deletions(-)