Remove CKEditor 4 support

We decided as maintainers to implement this in a 3.0 version.

I tested this and the countdown counter does not update as I enter text into a formatted text field with CKEditor 5. The same thing happens in the 3.0.x branch in general, before applying this merge request. When I save the node and then return to edit the node, the character count starts at the correct count, but then does not update as I type.

Strange because I checked with multiple CKEditor 5 editors on the page and it was working fine. Nonetheless, it is covered with tests.
Can you re-check your setup or give more information about your environment in question?

Changes looks good to me.

I've tested this as an editor and it works as expected. Marking reviewed and tested by the community.

Throwing another +1 to the MR, tested it and reviewed the code and all looks good.

Thank you all! Will be released as a beta release today.

Automatically closed - issue fixed for 2 weeks with no activity.