server-side deleted articles are not deleted on android

### Actual behaviour
- I deleted articles with the webapp. After syncing the android app, the deleted articles are still in the list. I tried all synchronisation methods. Setting up the android app on a new device did not download the deleted articles neither do they appear somewhere in the webapp.

### Expected behaviour
- The deleted article is removed from the list in the android app.

# Steps to reproduce the issue
1. wallabag some random article
2. synchronize your android app
3. delete the random article using the webapp
4. synchronize your android app: the article is still there

# Environment details
- **wallabag app version**: 2.1.0
- **wallabag app installation source** (e.g. Gplay, F-Droid, manual): f-droid
- **Android OS version**: 4.2.2
- **Android ROM** (e.g. stock, LineageOS, SlimRom,…): inkbook's android (e.g., no google play services)
- **Android hardware**: [inkbook prime](https://www.inkbook.eu/products)
- **wallabag server version**: 2.3.6
- **Do you have Two-Factor-Authentication enabled?**: no

# Your experience with wallabag Android app
Thanks a lot for the whole wallabag experience! It makes me read the web with self-hosted, open-source services. Many thanks :)!