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