Remove share buttons

About 0.19% of visitors in the past 12 months have clicked the share
buttons at all. The code is a little ugly, and it wastes a tiny bit of
space at the bottom of the page. I don't think it's really worth having.

And I think people probably print a page through the browser UI anyways.

assets/js/share-event.js

@@ -1,3 +0,0 @@
-function share_event(service) {
-    plausible("Share", {props: {Network: service}});
-}