x86, cleanup: Remove obsolete boot_cpu_id variable

boot_cpu_id is there for historical reasons and was renamed to
boot_cpu_physical_apicid in patch:

 c70dcb7 x86: change boot_cpu_id to boot_cpu_physical_apicid

However, there are some remaining occurrences of boot_cpu_id that are
never touched in the kernel and thus its value is always 0.

This patch removes boot_cpu_id completely.

Signed-off-by: Robert Richter <robert.richter@amd.com>
LKML-Reference: <1279731838-1522-8-git-send-email-robert.richter@amd.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
diff --git a/arch/x86/kernel/apb_timer.c b/arch/x86/kernel/apb_timer.c
index 8dd7780..08f75fb 100644
--- a/arch/x86/kernel/apb_timer.c
+++ b/arch/x86/kernel/apb_timer.c
@@ -343,7 +343,7 @@
 
 	/* Don't register boot CPU clockevent */
 	cpu = smp_processor_id();
-	if (cpu == boot_cpu_id)
+	if (!cpu)
 		return;
 	/*
 	 * We need to calculate the scaled math multiplication factor for