staging: comedi: amplc_pci230: remove PCI230_TEST_BIT()

The `PCI230_TEST_BIT()` macro is never used.  Remove it.

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