Deprecate the pam_console/pam_foreground flag-file directory

Deprecate the pam_console/pam_foreground flag-file directory

This feature is now compile-time conditional, and off by default.

pam_console appears to have been in Fedora and Gentoo until 2007.
pam_foreground seems to be specific to Debian and Ubuntu, where it was
unmaintained since 2008 and removed in 2010. The replacement for both
was ConsoleKit, which has itself been superseded by systemd-logind and
ConsoleKit2.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Bug: https://bugs.freedesktop.org/101629
Reviewed-by: Philip Withnall <withnall@endlessm.com>