OpObserver::onRenameCollection() dropTarget boolean argument is redundant

With UUIDs enabled by default, the dropped target collection UUID passed to the OpObserver::onRenameCollection() function is sufficient to infer the dropTarget state of the collection rename.

This change should not be back ported to 3.6 because we may still need to generate renameCollection oplog entries with a boolean dropTarget field in the absence of UUIDs.