Reduced Objective:

Remove YieldableCollectionIterator and deprecated constructor from CollectionTruncateMarkers.

This is a subset of the original goal to simplify the CollectionTruncateMarkers API. At this time, we are prioritizing other work over making additional improvements on the API.

Original Title/ Description: Simplify CollectionTruncateMarkers API
CollectionTruncateMarkers are used for the oplog and pre-images collection. Recently, support was removed for ChangeCollections. 

The API could be improved by removing subclass specific code, such as the UnyieldableCollectionIterator. Additionally, the API could benefit from additional comments, clearer names, and complex logic pushed down to its subclasses.