Fixing false assumption in TuneCassandra regarding setting compatibility

Previously, there was logic to guard against yaml config settings that had been added or removed from different versions. This was tested by adding a null check to see if the setting existed in the yaml that was read in. Unfortunately, if a property was commented out in the yaml (yet still compltetly valid as a setting) the entry would not be present in the map that snakeyaml produced, and hence you could never write out that setting. Basically this was a poor man's way to avoid branching. Now that we branch in priam, that is no longer necessary.