ARM: KVM: remove dead prototype for __kvm_tlb_flush_vmid

__kvm_tlb_flush_vmid has been renamed to __kvm_tlb_flush_vmid_ipa,
and the old prototype should have been removed when the code was
modified.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>