system: comment cleanups
system: comment cleanups

The "mschapv2" code referenced was removed in 2b17ad9077 and
additional dead code in bd2d28c6223.

See also: https://github.com/pfsense/pfsense/commit/651d468705

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core