cask/installer: remove migration symlinks on uninstall

Library/Homebrew/cask/installer.rb

@@ -792,10 +792,10 @@ on_request: true)
 
       if installed_caskfile&.exist?
         begin
-          @cask = CaskLoader.load(installed_caskfile)
+          @cask = CaskLoader.load_from_installed_caskfile(installed_caskfile)
           return
-        rescue CaskInvalidError
-          # could be caused by trying to load outdated caskfile
+        rescue CaskInvalidError, CaskUnavailableError
+          # could be caused by trying to load outdated or deleted caskfile
         end
       end
 

Library/Homebrew/cask/migrator.rb

@@ -80,7 +80,6 @@ module Cask
       when ".json"
         json = JSON.parse(path.read)
         json["token"] = new_token
-        json["old_tokens"] = [old_token, *json["old_tokens"]].compact.uniq
         path.atomic_write json.to_json
       end
     end