Seems to be a bug that the disable image upload options does not.
to disable the file manager, comment the following line in the admin_cms/contents_updates.php and contents_insert.php
$CKEditor_config["filebrowserBrowseUrl"] = "../webassist/kfm/index.php?uicolor=".urlencode(isset($CKEditor_config["uiColor"])?str_replace("#","#",$CKEditor_config["uiColor"]):"#eee")."&theme=webassist_v2";