entry/64: Remove unused ZERO_EXTRA_REGS macro

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Link: http://lkml.kernel.org/r/20161020120704.24042-1-kuleshovmail@gmail.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>