pgsql: Remove RI fast-path code for calling cast functions

Remove RI fast-path code for calling cast functions

The previous commit stopped using the fast path when FK values need a
cast function, which leaves its code for calling them unused. So
remove the following: the cached FmgrInfos for the cast and equality
functions and the memory context they used, the cast step in
build_index_scankeys(), the EXECUTE privilege check on the cast
function, and the unused forward declaration of RI_CompareHashEntry.

Also revert the changes made to ri_HashCompareOp() for the fast path's
cross-type operators and domain-typed keys in commits 2da86c1ef9 and
68ace967c1. Fast-path code no longer uses the function.

Reviewed-by: Matheus Alcantara <matheusssilv97(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAM527d9BgPjeOOYmbCBTd57R145qHCk-dzw9qNq+nOrDq1j__A@mail.gmail.com
Backpatch-through: 19

Branch
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REL_19_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2e42f11b6c883bf43cdd6d3329f3025e7096ca38

Modified Files
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src/backend/utils/adt/ri_triggers.c | 137 ++++++++++--------------------------
1 file changed, 39 insertions(+), 98 deletions(-)