cr_cansee(9): cr_bsd_visible() impacts, simplifications

Remove references to cr_canseeothergids(9) and cr_canseeotheruids(9).
Defer to cr_bsd_visible() for controlling sysctl(8) variables.

Reviewed by: bcr, mhorne
MFC after: 2 weeks
Sponsored by: Kumacom SAS
Differential Revision: https://reviews.freebsd.org/D40636