These changes port the PAM module from gnome-keyring/pam to libsecret/pam.
Removed `start_daemon` and the dependent code altogether. Because,
gnome-keyring-daemon is launched by systemd.
Replaced calls to `pam_get_item` to retrieve authentication tokens with
`pam_get_authtok`.
Signed-off-by: Dhanuka Warusadura <dhanuka@gnome.org>
