This was discovered as fallout from SERVER-54434, which caused a few secondaryDelaySecs upgrade/downgrade tests to fail.

Checks like this use kLatest when allowing secondaryDelaySecs. However, once kLatest becomes 5.0, those checks will incorrectly exclude 4.9. We need to make sure the upgrade/downgrade and reconfig paths for the delay field name work as expected when 4.9 becomes last-continuous.

This is specifically an issue for upgrading shardsvrs from 4.4 to 4.9 and for downgrading shardsvrs from 5.0 to 4.9 where 4.9 is last-continuous and 5.0 is latest.