Fix interrupt load balancing regression, introduced in revision

222813, that left all un-pinned interrupts assigned to CPU 0.

sys/x86/x86/intr_machdep.c:
	In intr_shuffle_irqs(), remove CPU_SETOF() call that initialized
	the "intr_cpus" cpuset to only contain CPU0.

	This initialization is too late and nullifies the results of calls
	the intr_add_cpu() that occur much earlier in the boot process.
	Since "intr_cpus" is statically initialized to the empty set, and
	all processors, including the BSP, already add themselves to
	"intr_cpus" no special initialization for the BSP is necessary.

MFC after:	3 days

sys/x86/x86/intr_machdep.c

@@ -525,9 +525,6 @@ intr_shuffle_irqs(void *arg __unused)
 	return;
 #endif
 
-	/* The BSP is always a valid target. */
-	CPU_SETOF(0, &intr_cpus);
-
 	/* Don't bother on UP. */
 	if (mp_ncpus == 1)
 		return;