consensus-formats: finish the format conversion

I unified the descriptions of the authority sections, so that they now use the same style as the rest of the document.

Also I discovered what seems to have been a mistake: the doc claimed that votes' authority sections contain shared-rand-{previous,current}-value. But they don't. Those are in the preamble. I looked at an actual vote to check...

Selecting @nickm as reviewer since we seem to have a shared expectation about this reformatting process which I guess we don't want to try to bring someone else up to speed on since it's nearly done now.