In SERVER-33017 we implemented a gossiping protocol to attach lastCommittedOpTime in every command reply. Additionally we were keeping track of the lastCommittedOpTime  for each shard in their respective ShardRemote objects.
Both gossiping and tracking of this field is not necessary anymore and can be now removed.

Supposition: this field is not necessary anymore because the lastCommitedOpTime have been included in the hello command response.