Revert "Issue #3072382 by Wim Leers: Update CKEditor to version 4.13"

core/assets/vendor/ckeditor/CHANGES.md

core/assets/vendor/ckeditor/LICENSE.md

core/assets/vendor/ckeditor/build-config.js

core/assets/vendor/ckeditor/ckeditor.js

core/assets/vendor/ckeditor/lang/af.js

core/assets/vendor/ckeditor/lang/ar.js

core/assets/vendor/ckeditor/lang/az.js

core/assets/vendor/ckeditor/lang/bg.js

core/assets/vendor/ckeditor/lang/bn.js

core/assets/vendor/ckeditor/lang/bs.js

core/assets/vendor/ckeditor/lang/ca.js

core/assets/vendor/ckeditor/lang/cs.js

core/assets/vendor/ckeditor/lang/cy.js

core/assets/vendor/ckeditor/lang/da.js

core/assets/vendor/ckeditor/lang/de-ch.js

core/assets/vendor/ckeditor/lang/de.js

core/assets/vendor/ckeditor/lang/el.js

core/assets/vendor/ckeditor/lang/en-au.js

core/assets/vendor/ckeditor/lang/en-ca.js

core/assets/vendor/ckeditor/lang/en-gb.js