Previously made two trips (get and set) for each group of items from
an index key being removed. Now, we fetch indexes once at the beginning
and store the updated indexes once at the end.
There was a difference compared to the previous v0.10 implementation
regarding the get/set behaviour. On v0.11, we used to get only the items
separately for each index and update only that index. Even though it
might have been more efficient, trips to the db are still too expensive
so it didn't matter much in the end.
