Update WITH_PROFILE description as it is yet removed

GCC still wants to link against (for example) libc_p.a when -pg is in
use, and it's unclear when and how this will be addressed. Change the
WITH_PROFILE option description to claim that it may be removed from an
unspecified future version of FreeBSD, rather than FreeBSD 14.

Reported by: Steve Kargl
MFC after: 1 week
Sponsored by: The FreeBSD Foundation