security/fprint_demo: Remove, it's deprecated

See here: https://fprint.freedesktop.org/

fprint_demo is obsolete. Most features are integrated into fprintd’s
helpers, and libfprint has an examples section.

It also doesn't build with the latest libfprint anymore.

Co-authored-by: Sheng-Yi Hung <aokblast@freebsd.org>
Signed-off-by: Daniel Schaefer <dhs@frame.work>
PR: 280749
Sponsored by: Framework Computer Inc
Sponsored by: The FreeBSD Foundation
Pull Request: https://github.com/freebsd/freebsd-ports/pull/291