kvm tools: don't bother including linux/compiler.h

linux/compiler.h will never give us a definition for __compiler_offsetof
because __KERNEL__ isn't defined, so just use the simple definition that
we have already.

This patch removes the redundant code.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>