Make the ModuleMetadata installable.

This was a wrong attempt to circumvent a bug for which a classes.dex
file gets wrongly generated by soong. The resulting APK will have a
classes.dex until the underlying bug in soong is solved, but it should
be mostly harmless (tm) and small anyway.

Test: mm
Bug: 121278993
Bug: 121187951
Change-Id: Ia5a17a8d0ee432b414ae26bedb13be9a63b03108