iio: adc: pac1934: remove unused struct 'samp_rate_mapping'

'samp_rate_mapping' has been unused since the original
commit 0fb528c8 ("iio: adc: adding support for PAC193x").

Remove it.
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20240522230457.478156-3-linux@treblig.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/pac1934.c

@@ -227,11 +227,6 @@ struct pac1934_features {
 	const char	*name;
 };
 
-struct samp_rate_mapping {
-	u16 samp_rate;
-	u8 shift2value;
-};
-
 static const unsigned int samp_rate_map_tbl[] = {
 	[PAC1934_SAMP_1024SPS] = 1024,
 	[PAC1934_SAMP_256SPS] = 256,