pgsql: Remove extra copying of TupleDescs for heap_create_with_catalog

Remove extra copying of TupleDescs for heap_create_with_catalog

Some callers were creating copies of tuple descriptors to pass to that
function, stating in code comments that it was necessary because it
modified the passed descriptor. Code inspection reveals this not to be
true, and indeed not all callers are passing copies in the first place.
So remove the extra ones and the misleading comments about this behavior
as well.

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/a40a5d9468a5f9f11d355ebf07f7741f5c267588

Modified Files
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src/backend/commands/cluster.c | 9 +++------
src/backend/executor/execMain.c | 8 +-------
2 files changed, 4 insertions(+), 13 deletions(-)