Revert "xen/x86: Workaround 'x86/ioapic: Add register level checks to detect bogus io-apic entries'"

This reverts commit 2531d64b.

The two patches:
      x86/apic: Replace io_apic_ops with x86_io_apic_ops.
      xen/x86: Implement x86_apic_ops

take care of fixing it properly.
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>