ARM: dts: Drop old AD7946 dts in favor of the new one

The old device tree for AD7946 describes hardware in a way that is
substantially different and incompatible with how we currently describe
AD7946. On top of that, it uses a deprecated device driver compatible
string. We already have a new device tree for AD7946
(zynq-coraz7s-ad7946-pmdz.dts), which better describes AD7946 and uses the
new, upstreamed, device driver for PulSAR and similar ADCs. Drop the old
AD7946 dts in favor of the new one.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>

Author: machschmitt