pgsql: Remove some dead code in selfuncs.c

Remove some dead code in selfuncs.c

RelOptInfo.userid is the same for all relations in a given inheritance
tree, so the code in examine_variable() and example_simple_variable()
that repeats the ACL checks on the root parent rel instead of a given
leaf child relations need not recompute userid too.

Author: Amit Langote <amitlangote09(at)gmail(dot)com>
Reported-by: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Discussion: https://postgr.es/m/20221210201753.GA27893@telsasoft.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/438e6b7240905c8055f9e221187f2ac818876169

Modified Files
--------------
src/backend/optimizer/util/relnode.c | 1 -
src/backend/utils/adt/selfuncs.c | 42 ++++++++++++++----------------------
2 files changed, 16 insertions(+), 27 deletions(-)