obslog: make {succnodes} be full hex nodes It should be up to the user to shorten the nodeid as much or as little as they like.

obslog: remove now-unused code for plain styling We now always use a non-plain formatter for the non-local-filtering code paths, so we can remove the code for plain styling. I couldn't figure out how to replace the fm.formatlist() by something less about formatting, so I've only removed the irrelevant arguments from those calls.