Revert b2a459edf "Fix GRANTED BY support in REVOKE ROLE statements"

The reverted commit attempted to fix SQL specification compliance for
the cases which 6aaaa76b left.  This however broke existing behavior
which takes precedence over spec compliance so revert. The introduced
tests are left after the revert since the codepath isn't well covered.
Per bug report 17346. Backpatch down to 14 where it was introduced.
Reported-by: Andrew Bille <andrewbille@gmail.com>
Discussion: https://postgr.es/m/17346-f72b28bd1a341060@postgresql.org

src/backend/commands/user.c

@@ -1319,18 +1319,7 @@ GrantRole(GrantRoleStmt *stmt)
 	ListCell   *item;
 
 	if (stmt->grantor)
-	{
 		grantor = get_rolespec_oid(stmt->grantor, false);
-
-		/*
-		 * Currently, this clause is only for SQL compatibility, not very
-		 * interesting otherwise.
-		 */
-		if (grantor != GetUserId())
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("grantor must be current user")));
-	}
 	else
 		grantor = GetUserId();
 

src/backend/parser/gram.y

@@ -7181,7 +7181,6 @@ RevokeRoleStmt:
 					n->admin_opt = false;
 					n->granted_roles = $2;
 					n->grantee_roles = $4;
-					n->grantor = $5;
 					n->behavior = $6;
 					$$ = (Node*)n;
 				}
@@ -7192,7 +7191,6 @@ RevokeRoleStmt:
 					n->admin_opt = true;
 					n->granted_roles = $5;
 					n->grantee_roles = $7;
-					n->grantor = $8;
 					n->behavior = $9;
 					$$ = (Node*)n;
 				}

src/test/regress/expected/privileges.out

@@ -47,9 +47,7 @@ ALTER FUNCTION leak(integer,integer) OWNER TO regress_priv_user1;
 -- test owner privileges
 GRANT regress_priv_role TO regress_priv_user1 WITH ADMIN OPTION GRANTED BY CURRENT_ROLE;
 REVOKE ADMIN OPTION FOR regress_priv_role FROM regress_priv_user1 GRANTED BY foo; -- error
-ERROR:  role "foo" does not exist
 REVOKE ADMIN OPTION FOR regress_priv_role FROM regress_priv_user1 GRANTED BY regress_priv_user2; -- error
-ERROR:  grantor must be current user
 REVOKE ADMIN OPTION FOR regress_priv_role FROM regress_priv_user1 GRANTED BY CURRENT_USER;
 REVOKE regress_priv_role FROM regress_priv_user1 GRANTED BY CURRENT_ROLE;
 DROP ROLE regress_priv_role;