arm64: KVM: Drop VHE-specific HYP call stub

We now call VHE code directly, without going through any central
dispatching function. Let's drop that code.

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