Extract the general purpose logic that's not specific to WiredTiger to higher layers to remove the dependency on replication.

Copied from this PR: we need to move OplogTruncateMarkers to the repl directory. Then we remove the RecordStore dependency on TruncateMarkers entirely. As far as I can tell, the only functionality that the RecordStore depends on is:

• To check if we're updating a document on the oplog. This seems like a completely unnecessary dependency and could be replaced with a startup option instead.
• Updating the size after a capped truncate. This also seems like the caller could just do this work after calling the function.
• Updating markers on commit. This could be accomplished with an onCommit handler
• Clearing the markers on truncate. Just have the caller do this.
• Killing the background thread. This should just be done explicitly on shutdown.