Delete old 'sysctlfile' module & related detritus

This is a follow-up commit to change Ib294b691d, which replaced the
'sysctlfile' module with a new 'sysctl' module. Since the migration was
successful, we can delete the older module and some of its associated junk.

Change-Id: Ifa5f3021c2970a38ee94348e5e7219b252d9d78e