Remove edge case handling of version code storage prior to version code 24

[FabioTacke]

In order to support updating from a version prior to version code 24 we use a fallback mechanism that shouldn't be necessary anymore.

[FabioTacke]

The fallback has been removed in #13 but a fallback to version code 30 had to be introduced as the version code hasn't been saved before if no migration was necessary on app launch. This has been changed but we need to rely on the fallback for some time.