This commit removes the new optimized category style introduced in
previous commits (d37a0d40, 9a80d718 and 430c42ac), in favour of the
existent `categories_only`.
The new style is called `categories_only_optimized` and it is designed
to show only the parent categories, without any subcategories. This
works best for communities with many categories (over a thousand).
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
