Remove the avatars and read people by name again

Remove the avatars and read people by name again

The marks were harder to read than the names they replaced, so they are
gone: the account menu is back to the user icon, and the issue and
change tables, the profile, the directory and the contributor list all
say the account name.

This takes out everything that existed to draw a mark: the DiceBear
bundle and its licence file, the entry source that built it, the
Landscape style, avatar.go and its tests, the avatar template and its
three helper functions, the avatar palette in everforest.css and the
illustration rules in vole.css, and the app.js block that rendered and
re-rendered them on a theme change.

The tables keep the layout from the previous change — an author column
and an assignee column — because that part reads better with names too.
The assignee cells are the @name chips that already linked to the
filtered list.

`vole workflow run verify` passes, and the licence inventory is back to
one entry fewer.