x86/apic: Remove the unused struct apic::apic_id_mask field

The only user verify_local_APIC() had been removed by commit:

  4399c03c

 ("x86/apic: Remove verify_local_APIC()")

... so there is no need to keep it.

Signed-off-by: Wei Jiangang <weijg.fnst@cn.fujitsu.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boris.ostrovsky@oracle.com
Cc: bsd@redhat.com
Cc: david.vrabel@citrix.com
Cc: jgross@suse.com
Cc: konrad.wilk@oracle.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1468463046-20849-1-git-send-email-weijg.fnst@cn.fujitsu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>