staging/lustre: Remove unused osc_on_mdt function

This only makes sense on metadata server, so get rid of it.

Also remove now unused MDS_OSC_MAX_RIF_DEFAULT define

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>