Another option is to edit the /ClientScript/ckeditor-mojoconfig.js file
set
config.scayt_autoStartup = false;
and remove all entries you see for SpellChecker or Scayt in the toolbar definitions
then save the file as ckeditor-mojoconfig_v2.js
and add this to your user.config file
<add key="CKEditor:ConfigPath" value="~/ClientScript/ckeditor-mojoconfig_v2.js"/>
that way it will not be affected by the old script being in the browser cache
Best,
Joe