Integration manager can't be disabled.

**Describe the bug**
I don't want my matrix clients to use `scalar.vector.im` but I still need integrations enabled for the [sticker picker](https://github.com/maunium/stickerpicker) to work. In element-web/desktop this can be achieved via config.json setting the integration manager urls to an empty string.

In element-android I could in the past configure my integration manager via client well-known but this seems to not be working now or it doesn't work for disabling it.

I tried the following entries in my .well-known file:

Setting an empty list of integration managers:
```
"m.integrations": {
"managers": []
}
```

Setting empty urls for the integration manager:
```
"m.integrations": {
"managers": [{"ui_url": "", "api_url": ""}]
}
```

Setting an url that is guaranteed to not resolve:
```
"m.integrations": {
"managers": [{"ui_url": "invalid.", "api_url": "invalid."}]
}
```

After every change I logged out and cleared the app data and logged in again. After every change it still showed scalar as an integration manager. :-(

**Smartphone (please complete the following information):**
- Device: Nexus 5X
- OS: Android 8.1 (LOS)

**Additional context**
- App version and store 1.0.13-F
- Homeserver: bubu1.eu

Add any other context about the problem here.