ahci: st: Remove STiH416 dt example

This platform is being removed from the kernel so remove
the dt example.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Cc: <tj@kernel.org>
Cc: <robh+dt@kernel.org>
Cc: <linux-ide@vger.kernel.org>
Acked-by: Rob Herring <robh@kernel.org>