arm64: hyp-stub/KVM: Kill __hyp_get_vectors

Nobody is using __hyp_get_vectors anymore, so let's remove both
implementations (hyp-stub and KVM).

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