Useless code in ExecInitModifyTable

Commit d3cc37f1d801a6b5cad9bf179274a8d767f1ee50 added this to
ExecInitModifyTable:

+ /* The root table RT index is at the head of the partitioned_rels
list */
+ if (node->partitioned_rels)
+ {
+ Index root_rti;
+ Oid root_oid;
+
+ root_rti = linitial_int(node->partitioned_rels);
+ root_oid = getrelid(root_rti, estate->es_range_table);
+ rel = heap_open(root_oid, NoLock); /* locked by InitPlan */
+ }

but I noticed that that function doesn't use the relation descriptor at
all. Since partitioned_rels is given in case of an UPDATE/DELETE on a
partitioned table, the relation is opened in that case, but the relation
descriptor isn't referenced at all in initializing WITH CHECK OPTION
constraints and/or RETURNING projections. (The mtstate->resultRelinfo
array is referenced in those initialization, instead.) So, I'd like to
propose to remove this from that function. Attached is a patch for that.

Best regards,
Etsuro Fujita