pg_upgrade: Remove dead code

Remove code meant for upgrading to a particular version of PostgreSQL
9.0.  Since pg_upgrade only supports upgrading to the current major
version, this code is no longer useful.

src/bin/pg_upgrade/check.c

@@ -279,12 +279,6 @@ check_cluster_compatibility(bool live_check)
 	get_control_data(&new_cluster, false);
 	check_control_data(&old_cluster.controldata, &new_cluster.controldata);
 
-	/* Is it 9.0 but without tablespace directories? */
-	if (GET_MAJOR_VERSION(new_cluster.major_version) == 900 &&
-		new_cluster.controldata.cat_ver < TABLE_SPACE_SUBDIRS_CAT_VER)
-		pg_fatal("This utility can only upgrade to PostgreSQL version 9.0 after 2010-01-11\n"
-				 "because of backend API changes made during development.\n");
-
 	/* We read the real port number for PG >= 9.1 */
 	if (live_check && GET_MAJOR_VERSION(old_cluster.major_version) < 901 &&
 		old_cluster.port == DEF_PGUPORT)