Remove support for adding commands that take a const int arg

It was used for local player commands, but all of those have been moved to cgame.
cgame doesn't need to add "addbot" command

It's only usable from server console. Added by game vm.
Clean up adding and removing commands from VMs

Auto remove commands added by game and cgame VMs when shuting down the VM.
Game VM no longer manually removes commands.
Save pointer to function to run VM command. No longer have to ask each VM if they want to handle a cmd and then forward to server, now just give cmd to VM that added cmd.
Moved forwarding commands to server into cgame. (cgame adds the commands; so it should handle them. Allows Cmd_ExecuteString to be cleaner.)
Only allow VM to remove commands it added (previously VMs could remove each others commands).