Remove multiple command validation as cpuinfo requires it

"criu cpuinfo [dump | check]" can't be used through the command line as this validation kicks in.
Other commands will fail due to required arguments so I believe it's not necessary anymore.

Signed-off-by: Marcos Lilljedahl <marcosnils@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>