api/highavailability: Stop sending model tag
api/highavailability: Stop sending model tag

It never made sense and is no longer checked server side. It wasn't
being tested here either.

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