Remove Firebase JavaScript SDK

Currently, Resell uses both the JavaScript Firebase SDK and the React Native Firebase library.

Based on the recent sign in bug, the JavaScript Firebase SDK behaves doesn't work so it should not be in use. Any part of our app that uses this fails, so we need to refactor this when we can. We also need some specific functionality of React Native Firebase, so since we are using that anyway, we should not have this inconsistency where we are relying on 2 different Firebase SDKs throughout the app.

We should completely remove the dependency on the JS Firebase SDK. You'll need to change `firebase.js` and other files that depend on it.

Let's start on this after we completely confirm that the JS Firebase SDK was causing the login issue though.

Begin by confirming the JavaScript Firebase SDK caused the login issue, then inspect firebase.js and the other files that depend on it. Trace those usages to identify the required changes and verify that the JavaScript SDK dependency is completely removed while the app continues using React Native Firebase.

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