KVM: arm64: Remove unused __extended_idmap_trampoline() prototype

__extended_idmap_trampoline() was removed a long time ago by
3421e9d8 ("arm64: KVM: Simplify HYP init/teardown") so remove the
unused function prototype.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201118194402.2892-4-will@kernel.org

arch/arm64/include/asm/kvm_host.h

@@ -58,7 +58,6 @@ int kvm_arm_init_sve(void);
 int __attribute_const__ kvm_target_cpu(void);
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
 void kvm_arm_vcpu_destroy(struct kvm_vcpu *vcpu);
-void __extended_idmap_trampoline(phys_addr_t boot_pgd, phys_addr_t idmap_start);
 
 struct kvm_vmid {
 	/* The VMID generation used for the virt. memory system */