Moving emulator-specific properties to /system_ext

We're now adding a core CSI system.img that is common across different
targets. So emulator-specific things should be moved to /system_ext.

Bug: 137711197
Test: build and checks those properties are in /system_ext/build.prop
Change-Id: I0f8afdeda77849b06842dd4f6cd04b7aab08ada4