staging/lustre: Remove server data from struct obd_export

Despite it's name struct obd_export could exist on the client too
(used for reverse exports), but all the actual server bits
are not needed there, so could be dropped. This is mostly
various target-related stuff.

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