staging/lustre: remove md_object.h

The declarations from lustre/include/md_object.h are not used so
remove them.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>