staging: lustre: remove l_wait_event() and related code

These macros are no longer used, so they can
be removed.

Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Patrick Farrell <paf@cray.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>