SDK - drop handling of legacy storage from old versions

[weilbith]

Description

Many versions ago we replaced the storage solution with a new architecture using a proper database as persistent storage layer. Though we still had to migrate old states which where stored at plain localStorage. Removing this handling is a breaking change. So we should do it with our next major release, which about to come. It will reduce the code base and simplifies it a little. Everyone who is still stuck on an old state needs to checkout any of the versions in-between to migrate, before switching to the most recent version.

Acceptance criteria

Tasks

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