Recent migration from the scrubber which did not comply fully with the documentation 
in regards to migration (through `swh db upgrade` cli) started some work to fix it .
The migration for the scrubber was fixed but broke some other modules as side-effects.
After further discussion with @douardda regarding the multiple proposed and somewhat
wrong implementations, we've come to an understanding and a proper plan to fix
- [x] Keep the current core code  (swh.core v2.10 with code and doc ok and aligned)
- [x] D7953: Fix swh.storage's datastore to add the attribute current_version
- [x] D7954: Fix swh.indexer's storage datastore to add the attribute current version
- [x] Drop unnecessary reverting diff  (again core code is actually ok providing ^)
- [x] Drop diff  which is irrelevant as it does not fix (I misunderstood the code)
- [x] D7958: Clean up unneeded code in scheduler