Remove Cask::Config#write.

Library/Homebrew/cask/config.rb

@@ -104,9 +104,5 @@ module Cask
         explicit: explicit,
       }.to_json(*args)
     end
-
-    def write(path)
-      path.atomic_write(to_json)
-    end
   end
 end

Library/Homebrew/cask/installer.rb

@@ -391,7 +391,7 @@ module Cask
     end
 
     def save_config_file
-      @cask.config.write(@cask.config_path)
+      @cask.config_path.atomic_write(@cask.config.to_json)
     end
 
     def uninstall