KVM: arm64: Remove unused declarations

Commit 53692908 ("KVM: arm/arm64: vgic: Fix source vcpu issues for GICv2 SGI")
removed vgic_v2_set_npie()/vgic_v3_set_npie() but not the declarations.
Commit 29eb5a3c ("KVM: arm64: Handle PtrAuth traps early") left behind
kvm_arm_vcpu_ptrauth_trap(), remove it.
Commit 2a0c3433 ("KVM: arm64: Initialize trap registers for protected VMs")
declared but never implemented kvm_init_protected_traps() and
commit cf5d3188 ("arm/arm64: KVM: Turn off vcpus on PSCI shutdown/reboot")
declared but never implemented force_vm_exit().

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Zenghui Yu <zenghui.yu@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230814140636.45988-1-yuehaibing@huawei.com