cups: allow unknown directives in conf files

cups: allow unknown directives in conf files

Patch for CVE-2025-61915 by mistake causes fatal error on unknown
directives in configuration files.
The default configuration already contains unknown directive in
non-systemd setups:
Unknown directive IdleExitTimeout on line 32 of /etc/cups/cupsd.conf

Backport fix for this from 2.4.x branch which reverts this behavior.

Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Paul Barker <paul@pbarker.dev>