Remove Ruby CA code and associated tests

In addition to removing the Ruby CLI for CA actions (see PUP-3648) and the CA-related settings from puppet.conf, we need to actually delete the underlying CA code and its associated tests. This will also allow us to remove some of the more complicated logic that had to be added to the SSL::Host class around ca_location (see https://github.com/puppetlabs/puppet/blob/master/lib/puppet/ssl/host.rb#L94-L114), since it will necessarily be remote once this removal has taken place. Likewise, we should be able to remove the various checks for whether or not we are the CA, simplifying logic elsewhere.