staging: comedi: addi_apci_1516: remove i_APCI1516_ConfigDigitalOutput()

The digital outputs of the board supported by this driver are not
configurable. This driver abuses the comedi API and uses the 'insn_config'
function of the digital output subdevice to enable/disable writing to
the eeprom on the board. Remove this function.

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