staging/lustre/ldlm: Drop unused blocking_refs flock field

blocking_refs is only used on the server, so drop it on the client.

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