p5-Canary::Stability: Provide only the FreeBSD stub

Canary::Stability continues to provide the same harmful instructions
that it has since 2013, including instructing users to uninstall Perl
and install one from 2015 (it also advises users to switch to an
unmaintained fork provided by the author).

Previously, there was an OPTION to install the actual module. There
is no scenario under which that should ever happen, so I'm removing
that entirely. This port now only provides a no-op stub.