Presumably, we did this because we don't have the information handily accessible. We get back the commit optime but not the wall time from the log service and so to get the wall time back we would probably need to query the oplog - which may not even be possible on a standby that hasn't fetched those entries yet.

The only consumers I see of this API right now are resharding_util and flow_control.

We should either:

1. Figure out how to return a real value here
2. See if those consumers can switch to use something besides wall time, and change the repl coord API to avoid future uses of this method in disagg 

impact: flow control needs to add signal & resharding may not complete correctly