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

(cherry picked from commit 82f9bc9ea8ed660c61050ad1d92f1a64108c7004)