Schleuder subscriber docs: fix rendering

It seems, inserting   breaks the rendering.

@init @paz Compare the current state of https://schleuder.org/schleuder/docs/subscribers.html#subscription-and-key-management and https://schleuder.org/dev/review/schleuder-website/schleuder-subscribers-fix-rendering/schleuder/docs/subscribers.html. Not really sure why inserting   leads to these results, but it seems removing this makes things work.

This example also shows that we should think about a better way to deploy for review, to check the proposed changes visually, for "external contributions".