Remove Robolectric and electricspock dependencies

[nrbrook]

electricspock is no longer maintained and the unit tests don't work with new Android Studio/gradle 7. In a project I develop which uses RxAndroidBle I switched to stubbing the android classes instead, which worked well. I'm currently doing the same for RxAndroidBle, and will create a PR when complete. Posting a feature request so we don't duplicate any work as we discussed using this approach before @dariuszseweryn.