iio: addac: ad74115: remove unused ad74115_dac_slew_rate_hz_tbl

This table was supposed to be used for handling the DAC rate, but it
ended up being unused. Remove it.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20221124152559.7895-1-cosmin.tanislav@analog.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>