Remove additional_plugins/alpha/ ? #936
Description
In https://github.com/s9y/additional_plugins is an alpha directory where we moved broken plugins into. It's not clear to me that this is still necessary given the version history git provides, and we haven't done so for all plugins, some we just removed. The purpose might have been to make the plugins easier to revive, by providing visibility, but I don't think that has ever happened.
Should we remove that directory?