Implement new MurderPlayer logic

Implement new MurderPlayer logic

In 2021.11.9, the host now uses MurderPlayer instead of impostors.
Impostor now use CheckMurder to request the host to kill a player. This
allows the host to prevent the target of the Guardian Angel from dying.

However, if the impostor that is checking the kill is also the host, AU
internally processes the CheckMurder RPC and sends the MurderPlayer RPC
first, *then* it sends the CheckMurder RPC.