apiserver/highavailability: Hide EnableHASingle
apiserver/highavailability: Hide EnableHASingle

This function is no longer called outside the package. Removed the
misleading docstring too.

gabriel-samfira/juju,mjs/juju,perrito666/juju,mjs/juju,anastasiamac/juju,gabriel-samfira/juju,marcmolla/juju,macgreagoir/juju,mjs/juju,anastasiamac/juju,waigani/juju,ericsnowcurrently/juju,howbazaar/juju,anastasiamac/juju,reedobrien/juju,frankban/juju,howbazaar/juju,gabriel-samfira/juju,marcmolla/juju,dimitern/juju,howbazaar/juju,dimitern/juju,frankban/juju,reedobrien/juju,frankban/juju,alesstimec/juju,alesstimec/juju,ericsnowcurrently/juju,mikemccracken/juju,mikemccracken/juju,marcmolla/juju,anastasiamac/juju,perrito666/juju,alesstimec/juju,dimitern/juju,alesstimec/juju,mikemccracken/juju,waigani/juju,perrito666/juju,macgreagoir/juju,waigani/juju,reedobrien/juju,macgreagoir/juju,anastasiamac/juju,dimitern/juju,mjs/juju,gabriel-samfira/juju,mikemccracken/juju,AdamIsrael/juju,bac/juju,perrito666/juju,marcmolla/juju,frankban/juju,howbazaar/juju,ericsnowcurrently/juju,mikemccracken/juju,ericsnowcurrently/juju,bac/juju,howbazaar/juju,perrito666/juju,AdamIsrael/juju,reedobrien/juju,ericsnowcurrently/juju,macgreagoir/juju,mjs/juju,bac/juju,mjs/juju,frankban/juju,mjs/juju,marcmolla/juju,macgreagoir/juju,gabriel-samfira/juju,reedobrien/juju,AdamIsrael/juju,dimitern/juju,AdamIsrael/juju,bac/juju,bac/juju,alesstimec/juju,waigani/juju