Remove unnecessary [{topic}] tag

[awailly]

The "[{topic}]" tag before [sect1] is not needed. All topic roles contain the same word, and is now the default. Thus, all [sect1] titles have the "topic" tag as default.

[mojavelinux]

I require the topic role intentionally because it controls whether or not the title is shown for a slide (and if it is shown, how). I agree, though, that it need not only be a topic role that controls whether the title is shown. In other words, some redesign is needed here.