Remove extra copying of TupleDescs for heap_create_with_catalog

Some callers were creating copies of tuple descriptors to pass to that
function, stating in code comments that it was necessary because it
modified the passed descriptor.  Code inspection reveals this not to be
true, and indeed not all callers are passing copies in the first place.
So remove the extra ones and the misleading comments about this behavior
as well.

src/backend/commands/cluster.c

@@ -591,8 +591,7 @@ rebuild_relation(Relation OldHeap, Oid indexOid,
 Oid
 make_new_heap(Oid OIDOldHeap, Oid NewTableSpace)
 {
-	TupleDesc	OldHeapDesc,
-				tupdesc;
+	TupleDesc	OldHeapDesc;
 	char		NewHeapName[NAMEDATALEN];
 	Oid			OIDNewHeap;
 	Oid			toastid;
@@ -605,13 +604,11 @@ make_new_heap(Oid OIDOldHeap, Oid NewTableSpace)
 	OldHeapDesc = RelationGetDescr(OldHeap);
 
 	/*
-	 * Need to make a copy of the tuple descriptor, since
-	 * heap_create_with_catalog modifies it.  Note that the NewHeap will not
+	 * Note that the NewHeap will not
 	 * receive any of the defaults or constraints associated with the OldHeap;
 	 * we don't need 'em, and there's no reason to spend cycles inserting them
 	 * into the catalogs only to delete them.
 	 */
-	tupdesc = CreateTupleDescCopy(OldHeapDesc);
 
 	/*
 	 * But we do want to use reloptions of the old heap for new heap.
@@ -645,7 +642,7 @@ make_new_heap(Oid OIDOldHeap, Oid NewTableSpace)
 										  InvalidOid,
 										  InvalidOid,
 										  OldHeap->rd_rel->relowner,
-										  tupdesc,
+										  OldHeapDesc,
 										  NIL,
 										  OldHeap->rd_rel->relkind,
 										  OldHeap->rd_rel->relpersistence,

src/backend/executor/execMain.c

@@ -2394,7 +2394,6 @@ OpenIntoRel(QueryDesc *queryDesc)
 	Oid			tablespaceId;
 	Datum		reloptions;
 	Oid			intoRelationId;
-	TupleDesc	tupdesc;
 	DR_intorel *myState;
 	static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
 
@@ -2467,9 +2466,6 @@ OpenIntoRel(QueryDesc *queryDesc)
 									 false);
 	(void) heap_reloptions(RELKIND_RELATION, reloptions, true);
 
-	/* Copy the tupdesc because heap_create_with_catalog modifies it */
-	tupdesc = CreateTupleDescCopy(queryDesc->tupDesc);
-
 	/* Now we can actually create the new relation */
 	intoRelationId = heap_create_with_catalog(intoName,
 											  namespaceId,
@@ -2478,7 +2474,7 @@ OpenIntoRel(QueryDesc *queryDesc)
 											  InvalidOid,
 											  InvalidOid,
 											  GetUserId(),
-											  tupdesc,
+											  queryDesc->tupDesc,
 											  NIL,
 											  RELKIND_RELATION,
 											  into->rel->relpersistence,
@@ -2492,8 +2488,6 @@ OpenIntoRel(QueryDesc *queryDesc)
 											  allowSystemTableMods);
 	Assert(intoRelationId != InvalidOid);
 
-	FreeTupleDesc(tupdesc);
-
 	/*
 	 * Advance command counter so that the newly-created relation's catalog
 	 * tuples will be visible to heap_open.