dt-bindings: iio: asahi-kasei,ak8975: drop incorrect AK09116 compatible

All compatibles in this binding without prefixes were deprecated, so
adding a new deprecated one after some time is not allowed, because it
defies the core logic of deprecating things.

Drop the AK09916 vendorless compatible.

Fixes: 76e28aa97fa0 ("iio: magnetometer: ak8975: add AK09116 support")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20240806053016.6401-2-krzysztof.kozlowski@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>