We added size limit checks when adding data-bearing node metrics to the distinct command response in SERVER-90651. We skip adding the metrics if we are too close to the size limit. The mongos distinct path also has some non-trivial logic to handle the case where it doesn't get metrics back due to this. 

In SERVER-93216, we learned that this special handling is unnecessary, because we actually have some buffer beyond the 16MB limit to return the metrics (the real internal limit is bigger). We should remove the special handling for distinct and the associated tests (the test added SERVER-93216 already covers this case for distinct as much as is needed).