staging:iio:cdc:ad7150: Remove magnitude adaptive events

The devices support window detection, but that corresponds to
being outside of a range defined by a lower an uppper bound rather
than being related to magnitude as such.   Hence drop this interface
in the interests of making the driver ABI compliant.

We may bring back support for the window mode at somepoint in the future
but it will be in an ABI compliant fashion.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210314181511.531414-3-jic23@kernel.org