Assuming we are not removing the mongod SNMP interface for 4.2, we may want to mark the (MMAPv1) metrics that set _backgroundFlushingOnly or _journalOnly as deprecated. Even
if we aren't removing, deprecation is not required to allow for user to request stats and for our tests to pass. It would only be there for to add clarity.

To deprecate metrics you can:

1. Add the "DEPRECATED" tag to each metric that sets one or both of the above to true
2. For each of those metrics, change the corresponding "STATUS" tag in docs/MONGOD-MIB.txt to "deprecated".