Check which assets can be deleted

[LeandraH]

Is your feature request related to a problem? Please describe. We might have some assets (probably mainly images) that are not necessary anymore. One example is probably all the files named launch_screen.png in varying folders in native/android/app/src/main/res.

Describe the solution you'd like We should check:

• [ ] which assets in the Android folders (native/android/app/src/main/res) are unneeded
• [ ] which assets in the iOS folders (native/ios/Integreat/Images.xcassets) are unneeded
• [ ] which assets in the shared folders (build-configs) are unneeded
• [ ] if we have assets just for web (didn't find any at a quick search) and check those as well
• [ ] if we can replace png files with svg ones

Describe alternatives you've considered It's really more of a clean-up, we could also not.

[steffenkleinle]

I already cleaned up the android assets a little in #2757.