x86: kernel/setup_32.c: unexport machine_id

This patch removes the unused EXPORT_SYMBOL(machine_id).

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>