staging/lustre: Remove struct ll_iattr

This was a compat code from the time it had ia_attr_flags.
Instead convert all the cryptic callers that did
((struct ll_iattr *)&op_data->op_attr)->ia_attr_flags into
direct access to op_data->op_attr_flags

This also makes lustre/include/linux/obd.h not needed anymore,
so remove it.

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