Improve some comments in pg_upgrade.c

When restoring database schemas on a new cluster, database "template1"
is processed first, followed by all other databases in parallel,
including "postgres".  Both "postgres" and "template1" have some extra
handling to propagate each one's properties, but comments were confusing
regarding which one is processed where.

Author: Julien Rouhaud
Reviewed-by: Daniel Gustafsson
Discussion: https://postgr.es/m/CAOBaU_a2iviTG7FE10yO_gcW+zQCHNFhRA_NDiktf3UR65BHdw@mail.gmail.com

src/bin/pg_upgrade/pg_upgrade.c

@@ -341,10 +341,9 @@ create_new_objects(void)
 		snprintf(log_file_name, sizeof(log_file_name), DB_DUMP_LOG_FILE_MASK, old_db->db_oid);
 
 		/*
-		 * template1 and postgres databases will already exist in the target
-		 * installation, so tell pg_restore to drop and recreate them;
-		 * otherwise we would fail to propagate their database-level
-		 * properties.
+		 * template1 database will already exist in the target installation,
+		 * so tell pg_restore to drop and recreate it; otherwise we would fail
+		 * to propagate its database-level properties.
 		 */
 		create_opts = "--clean --create";
 
@@ -378,10 +377,9 @@ create_new_objects(void)
 		snprintf(log_file_name, sizeof(log_file_name), DB_DUMP_LOG_FILE_MASK, old_db->db_oid);
 
 		/*
-		 * template1 and postgres databases will already exist in the target
-		 * installation, so tell pg_restore to drop and recreate them;
-		 * otherwise we would fail to propagate their database-level
-		 * properties.
+		 * postgres database will already exist in the target installation, so
+		 * tell pg_restore to drop and recreate it; otherwise we would fail to
+		 * propagate its database-level properties.
 		 */
 		if (strcmp(old_db->db_name, "postgres") == 0)
 			create_opts = "--clean --create";