Quieten warnings about unused variables

These variables are only ever written to in assertion-enabled builds,
and the latest Microsoft compilers complain about such variables in
non-assertion-enabled builds.

Apparently they don't worry so much about variables that are written to
but not read from, so most of our PG_USED_FOR_ASSERTS_ONLY variables
don't cause the problem.

Discussion: https://postgr.es/m/7800.1505950322@sss.pgh.pa.us

src/backend/optimizer/path/costsize.c

@@ -4550,15 +4550,11 @@ set_subquery_size_estimates(PlannerInfo *root, RelOptInfo *rel)
 {
 	PlannerInfo *subroot = rel->subroot;
 	RelOptInfo *sub_final_rel;
-	RangeTblEntry *rte PG_USED_FOR_ASSERTS_ONLY;
 	ListCell   *lc;
 
 	/* Should only be applied to base relations that are subqueries */
 	Assert(rel->relid > 0);
-#ifdef USE_ASSERT_CHECKING
-	rte = planner_rt_fetch(rel->relid, root);
-	Assert(rte->rtekind == RTE_SUBQUERY);
-#endif
+	Assert(planner_rt_fetch(rel->relid, root)->rtekind == RTE_SUBQUERY);
 
 	/*
 	 * Copy raw number of output rows from subquery.  All of its paths should
@@ -4670,14 +4666,9 @@ set_function_size_estimates(PlannerInfo *root, RelOptInfo *rel)
 void
 set_tablefunc_size_estimates(PlannerInfo *root, RelOptInfo *rel)
 {
-	RangeTblEntry *rte PG_USED_FOR_ASSERTS_ONLY;
-
 	/* Should only be applied to base relations that are functions */
 	Assert(rel->relid > 0);
-#ifdef USE_ASSERT_CHECKING
-	rte = planner_rt_fetch(rel->relid, root);
-	Assert(rte->rtekind == RTE_TABLEFUNC);
-#endif
+	Assert(planner_rt_fetch(rel->relid, root)->rtekind == RTE_TABLEFUNC);
 
 	rel->tuples = 100;