staging: comedi: ni_stc.h: remove unused members from struct ni_private

Remove all the unsed members from the private data for the ni mio drivers.

The ao0p and ao1p members are only used in the ni_ao_reset() function and
the code is commented out. Remove them, and the commented out code, as well.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>