clean up hostnames values

Aside from READMEs and values files, since !89 (merged) the "hostnames" values don't appear to be used anywhere except by utils.qdbcluster_hostname in ./utils/templates/_hostnames.tpl which may still be worth keeping (though do you really need so many ways to change the QDB name when the Release name should do the trick?)

Anyway aside from the QDB case there are a bunch of other "hostnames" not used that should be cleaned up.