Firebase Android SDKs for Auth, Database, Storage, Functions do not require Google Play Services anymore.
https://firebase.google.com/docs/android/android-play-services

Removing checks for Google Play services for these products from the C++ SDK.
Tested by running integration tests on,

• devices with Google play services (https://github.com/firebase/firebase-cpp-sdk/actions/runs/730345555)
• devices without Google Play services (tested on Kindle)
• android emulator images with and without google play services.

Addresses firebase/quickstart-unity#975