iio: adc: ad_sigma_delta: remove ad_sd_{setup,cleanup}_buffer_and_trigger()

iio: adc: ad_sigma_delta: remove ad_sd_{setup,cleanup}_buffer_and_trigger()

Since all AD Sigma-Delta drivers now use the
devm_ad_sd_setup_buffer_and_trigger() function, we can remove the old
ad_sd_{setup,cleanup}_buffer_and_trigger() functions.

This way we can discourage new drivers that use the ad_sigma_delta
lib-driver to use these (older functions).

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210513120752.90074-13-aardelean@deviqon.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>