internal/exec/stages/disks: remove old comment
internal/exec/stages/disks: remove old comment

RAID devices are no longer autostarted when ignition is running. This
comment no longer applies.

coreos/ignition,coreos/ignition,dgonyeo/ignition,ajeddeloh/ignition,ajeddeloh/ignition,ajeddeloh/ignition,dgonyeo/ignition,dgonyeo/ignition,coreos/ignition