Remove impl from InputClassifier HAL

Make the reference implementation for InputClassifier HAL do nothing.
This is to allow cuttlefish to install this implementation.

It is safe for any device to install this implementation, and is
equivalent to not having the HAL running at all.

Test: boot up cuttlefish, and interact with the virtual device to ensure
that input works okay. Then 'ps -A | grep -i input' and ensure that the
HAL is running on the device.
Bug: 122600147

Change-Id: I841811bc0da3d78db8d7c1589cf1c59819d901a1