arm64: KVM: Cleanup asm-offset.c

As we've now rewritten most of our code-base in C, most of the
KVM-specific code in asm-offset.c is useless. Delete-time again!

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>