staging:iio:lis3l02dq drop separate driver

Retire this venerable driver as the basic support is now in the
generic st-sensors accelerometer driver.

There are a few missing features in the new driver:
* Threshold events.
* Access to the calibration adjustment registers (patch shortly)

In exchange it brings a cleaner and more maintainable code base that actually
gets tested more than once every few years.  I'll actually be suprised
if anyone other than me has a board with one of these on that is running
an up to date kernel.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>