Don't show HTML in Hansard appearance excerpts

This suppresses the `<p>` tags that appear on pages like this:

  http://www.pa.org.za/person/cameron-mackenzie/

As discussed in IRC, there's also the possibility that the `truncatewords:50` filter could cut off the `</p>` tag and therefore end up with invalid markup, which has happened on http://www.pa.org.za/person/cameron-mackenzie/ in the first Plenary Appearance.