Remove addition of cell toolbar reminder

Follow up from PR #2331

Author: takluyver

notebook/static/notebook/js/maintoolbar.js

@@ -55,8 +55,7 @@ define([
             ],
             'run_int'],
          ['<add_celltype_list>'],
-         [['jupyter-notebook:show-command-palette']],
-         ['<add_celltoolbar_reminder>']
+         [['jupyter-notebook:show-command-palette']]
         ];
         this.construct(grps);
     };