Currently, as part of FCV downgrade, we're dropping the global indexes collection. However, we shouldn't drop global indexes information if the user still has global indexes. Instead, we should abort downgrade with an error if the user tries to downgrade and still has global indexes.

Once we are sure that the user has no global indexes, we still need to drop the global indexes collections, but we also need to clear the in memory state relating to global indexes in the CSR.