KVM: arm64: nv: Drop EL12 register traps that are redirected to VNCR

With FEAT_NV2, a bunch of system register writes are turned into
memory writes. This is specially the fate of the EL12 registers
that the guest hypervisor manipulates out of context.

Remove the trap descriptors for those, as they are never going
to be used again.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>