From FCKeditor Docs

Not all files are required by the editor to run, and you could reduce the number and size of the files to be published in a production environment by removing:

• All directories that start with one underscore (like _docs and _sample) including "editor/_source".
• Any skin you are not using from the "editor/skins" directory.
• Any "smiley" collection you are not using from the "editor/images/smiley" directory.
• Any plugin you don't need from the "editor/plugins" directory.
• Any connector you don't need from the "editor/filemanager/connectors" directory.
• Any "fckeditor.ext" file you don't need from the root of the editor package (based on your server side language).
• Any "<lang>.js" file you don't need from the "editor/lang" directory (only if AutoDetectLanguage = false).

At a minimum, there should be 4 files in the root FCKeditor folder: fckeditor.php (or other extensions), fckstyles.xml, fcktemplates.xml and fckconfig.js

NOTE: Do not remove the file "fckconfig.js"; otherwise the editor will not work and JavaScript errors could be thrown.