mate-desktop: Remove unused code.

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackware-id.org>
mate-panel: Remove unused code.

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackware-id.org>
mate-applets: Remove unused code.

Signed-off-by: Willy Sudiarto Raharjo <willysr@slackware-id.org>