Eliminate pip from collectd manifest

Our old manifests installed collectd via pip under the mistaken
impression that a newer version of collectd than is provided by
Ubuntu 12.04 was needed to use the carbon_writer plugin.  This
actually isn't the case, and the plugin included by the manifest
works just fine with the collectd packaged in 12.04.  Installing
via pip is problematic if you have poor proxies between yourself
and the internet, whereas installing via apt (like almost everything
else) is much less problematic.

Closes-Bug: #1215560