can't compile ankidroid using local_backend

trying to compile ankidroid with `local_backend=true`:
```
1: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':libanki:bundleDebugAar'.
> Error while evaluating property 'hasLocalAarDeps' of task ':libanki:bundleDebugAar'.
> Direct local .aar file dependencies are not supported when building an AAR. The resulting AAR would be broken because the classes and Android resources from any local .aar file dependencies would not be packaged in the resulting AAR. Previous versions of the Android Gradle Plugin produce broken AARs in this case too (despite not throwing this error). The following direct local .aar file dependencies of the :libanki project caused this error: /home/jake/code/Anki-Android-Backend/rsdroid/build/outputs/aar/rsdroid-release.aar
```

using a local maven repo solves this