x86/irq: Remove unused pre_init_apic_IRQ0()

Now there's no user of pre_init_apic_IRQ0(), so remove it.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Cohen <david.a.cohen@linux.intel.com>
Cc: Sander Eikelenboom <linux@eikelenboom.it>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dimitri Sivanich <sivanich@sgi.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Grant Likely <grant.likely@linaro.org>
Link: http://lkml.kernel.org/r/1428905519-23704-32-git-send-email-jiang.liu@linux.intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>