SERVER-67346 disabled autosplitting on the sessions collection because the new data-size balancing policy (landed in v6.0.3) is not chunk-based and splitting is not required anymore.

The ticket was aimed at landing only in v6.1 (as per the commit's title) hence we didn't make the effort to unset the noAutoSplit option on downgrade based on the assumption that there was low chance for users to perform a double downgrade getting back to v6.0 and then set the FCV down to v5.0.

However, the commit was then backported to v6.0 and at that point we should have introduced the logic to clear the flag up upon downgrading the FCV to v5.0. Purpose of this ticket is to implement that logic in the next v6.0 sub-version.

We should: clear out CollectionType::kMaxChunkSizeBytesFieldName and CollectionType::kNoAutoSplitFieldName from the document referring config.system.sessions in config.collections and avoid the periodic logical sessions refresher from setting those options again.