KVM: PPC: code cleanup for kvmppc_book3s_irqprio_deliver

This part was commented from commit 2f4cf5e4

 ("Add book3s.c")
in about 14 years before.
If there are no plans to enable this part code in the future,
we can remove this dead code.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240125083348.533883-1-chentao@kylinos.cn