(PDB-863) Remove com. from jmx and mq endpoints

This PR removes the com. from the jmx and mq endpoints so that these
endpoints use the new puppetlabs.puppetdb namespace. In order to change
all the outstanding references to the old namespace, this PR also
updates the dashboard index.html to reference the v4 metrics api.
@wkalt @kbarber @senior I wasn't sure if we still wanted to keep prefix as an argument here or if it's just safe to remove this.