artists: allow members to rename, delete, and undelete artists.

Also allow Members to edit deleted or banned artists. Previously this
was limited in the html, but not in the backend.

app/models/artist.rb

@@ -538,14 +538,6 @@ class Artist < ApplicationRecord
     end
   end
 
-  def deletable_by?(user)
-    user.is_builder?
-  end
-
-  def editable_by?(user)
-    user.is_builder? || (!is_banned? && is_active?)
-  end
-
   def visible?
     !is_banned? || CurrentUser.is_gold?
   end