Remove allowed_addons.json and the related tools

For the desktop-only 14.0a1, we've updated the NoScript version, but we didn't update the allowed_addons.json file that is used for checking the hash of its xpi.

We don't need that file anymore, since we don't have our custom addons provider, so we could stop updating it and remove the file to generate it (but we'll need to update the release preparation script to still query AMO for NoScript and uBlock Origin).