staging:iio:adc:ad7606 remove unused chip info elements.

These are now handled through the chan_spec arrays and no one
is using them anymore.

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>