timeline is not needed in BaseBackup()

This code was accidentally part of the patch, it's only
needed for the code that's for 9.2. Not needing the timeline
also removes the need to call IDENTIFY_SYSTEM.

Noted by Peter E.

src/bin/pg_basebackup/pg_basebackup.c

@@ -756,7 +756,6 @@ static void
 BaseBackup(void)
 {
 	PGresult   *res;
-	uint32		timeline;
 	char		current_path[MAXPGPATH];
 	char		escaped_label[MAXPGPATH];
 	int			i;
@@ -768,25 +767,6 @@ BaseBackup(void)
 	 */
 	conn = GetConnection();
 
-	/*
-	 * Run IDENFITY_SYSTEM so we can get the timeline
-	 */
-	res = PQexec(conn, "IDENTIFY_SYSTEM");
-	if (PQresultStatus(res) != PGRES_TUPLES_OK)
-	{
-		fprintf(stderr, _("%s: could not identify system: %s\n"),
-				progname, PQerrorMessage(conn));
-		disconnect_and_exit(1);
-	}
-	if (PQntuples(res) != 1)
-	{
-		fprintf(stderr, _("%s: could not identify system, got %i rows\n"),
-				progname, PQntuples(res));
-		disconnect_and_exit(1);
-	}
-	timeline = atoi(PQgetvalue(res, 0, 1));
-	PQclear(res);
-
 	/*
 	 * Start the actual backup
 	 */