staging:iio:meter: Remove unused macro IIO_DEV_ATTR_CH_OFF

This patch removes the macro IIO_DEV_ATTR_CH_OFF. The macro
IIO_DEV_ATTR_CH_OFF is not required, due to the replace of it by the
direct use of IIO_DEVICE_ATTR in files staging/iio/meter/ade7759.c and
staging/iio/meter/ade7753.c.

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/meter/meter.h

@@ -348,9 +348,6 @@
 #define IIO_DEV_ATTR_VPERIOD(_mode, _show, _store, _addr)		\
 	IIO_DEVICE_ATTR(vperiod, _mode, _show, _store, _addr)
 
-#define IIO_DEV_ATTR_CH_OFF(_num, _mode, _show, _store, _addr)		\
-	IIO_DEVICE_ATTR(choff_##_num, _mode, _show, _store, _addr)
-
 /* active energy register, AENERGY, is more than half full */
 #define IIO_EVENT_ATTR_AENERGY_HALF_FULL(_evlist, _show, _store, _mask) \
 	IIO_EVENT_ATTR_SH(aenergy_half_full, _evlist, _show, _store, _mask)