pgsql: Change get_constraint_index() to use pg_constraint.conindid

Change get_constraint_index() to use pg_constraint.conindid

It was still using a scan of pg_depend instead of using the conindid
column that has been added since.

Since it is now just a catalog lookup wrapper and not related to
pg_depend, move from pg_depend.c to lsyscache.c.

Reviewed-by: Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://www.postgresql.org/message-id/flat/4688d55c-9a2e-9a5a-d166-5f24fe0bf8db%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8b069ef5dca97cd737a5fd64c420df3cd61ec1c9

Modified Files
--------------
src/backend/catalog/pg_depend.c | 69 ------------------------------------
src/backend/commands/tablecmds.c | 1 -
src/backend/optimizer/util/plancat.c | 1 -
src/backend/utils/adt/ruleutils.c | 3 +-
src/backend/utils/cache/lsyscache.c | 27 ++++++++++++++
src/include/catalog/dependency.h | 2 --
src/include/utils/lsyscache.h | 1 +
7 files changed, 29 insertions(+), 75 deletions(-)