KVM: arm/arm64: vgic: Remove the declaration of kvm_send_userspace_msi()

The callsite of kvm_send_userspace_msi() is currently arch agnostic.
There seems no reason to keep an extra declaration of it in arm_vgic.h
(we already have one in include/linux/kvm_host.h).

Remove it.

Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Link: https://lore.kernel.org/r/20191029071919.177-2-yuzenghui@huawei.com