Crashytics plugin makes builds non-reproducible

### [REQUIRED] Step 2: Describe your environment

* Android Studio version: Android Studio Arctic Fox | 2020.3.1 Canary 12
* Firebase Component: Crashlytics
* Component version: 2.5.2

### [REQUIRED] Step 3: Describe the problem

#### Steps to reproduce:

1. Integrate crashlytics into an android app
2. Export an APK twice
3. Extract the contents of the APK and `diff -r` them. See:
```
76c76
< 79a4d6b75ce84bd6ae254b900862f3a4
---
> b8c86404219046eda8f32c66a3f45467
```

#### Expected

A determinsitic id to be used and two builds with the same source to have an equivalent build id. Possibly a hash of the mapping file could be used.