Do not use deprecated per_page_value_for_screen_size

Use the screen size independent items_per_page instead.

Author: tvdeyen

app/controllers/alchemy/admin/users_controller.rb

@@ -17,7 +17,7 @@ def index
         @query.sorts = 'login asc' if @query.sorts.empty?
         @users = @query.result
           .page(params[:page] || 1)
-          .per(per_page_value_for_screen_size)
+          .per(items_per_page)
       end
 
       def new