dropAggTempCollections drops the temporary collections listed on 'config.agg_temp_collections', in a sharding-aware way (i.e. by routing _shardsvrDropCollection to the db-primary shard). However, if the database has been dropped, this routing will fail with NamespaceNotFound. In this case, the temp colleciton was already dropped, so the collection should be delisted from 'config.agg_temp_collections'.