[DEVEX-185] Removed leftover folders that had KurrentDb instead of KurrentDB (#340)

It seems that after conflicts when merging StreamRevision PR, the code before merging stayed as duplicated without capital B in KurrentDb.

I checked by doing copying with override from those folders to the proper one, and there were no differences besides those stream revision changes, so it's safe to just remove them.

Author: oskardudycz