Fix update notification on latest foss version of ckeditor 4.22.*.

[corentinbettiol]

Hi. Ckeditor started to show a notification yesterday:

It's a problem because it shows on every ckeditor box, even the ones who are part of a form on a public-facing website: every visitor of the site will see this.

Since we can't use versions 4.23+ (those are lts versions, which needs a license key to work, they changed the license), what we can do as a temporary fix is simply remove the notification process on the ckeditor code (gnu gpl3, we're allowed to make changes to the program).