pg_replslot will only exist in 9.4 and later

We need to clean this up regardless of whether "use_replication_slots"
is set.

repmgr.c

@@ -1795,6 +1795,8 @@ stop_backup:
 		 * functionality of replication slots
 		 */
 
+		if (server_version_num >= 90400)
+		{
 			maxlen_snprintf(script, "rm -rf %s/pg_replslot/*",
 							local_data_directory);
 			r = system(script);
@@ -1805,6 +1807,7 @@ stop_backup:
 				exit(ERR_BAD_RSYNC);
 			}
 		}
+	}
 
 	/* Finally, write the recovery.conf file */
 	create_recovery_file(local_data_directory);