sysutils/sample: mark BROKEN and schedule for deprecation

Sample was abandoned upstream in 2016. It still builds on
11- and 12-, but after that the API for vm_page_unhold(page)
changed (function renamed, parameters different) so it's
broken on 13- and later. Give it a lengthy deprecation so
people will notice (I'm not sure how "deprecate because it
is tied to legacy releases" should work).

Discussed with wg@ by email.