Dear Jerrz,
Please open "\CuteSoft_Client\Gallery\Editor\Explorer\Code.js", and comment the following lines:
var newcatebtn=CreateEditorButton("Images/standard-category.png",GalleryLocalize.CLICK_NEWCATEGORY);
leftToolbar.appendChild(newcatebtn);
newcatebtn.onclick=function(){ browser.PromptNewCategory(); };
Thank you for asking