The question is in the title : How to remove buttons from CKeditor 4 .
Documentation does not answer it clearly
In config.js file inside scripts/ckeditor/ of your project, just do the following way
config.removePlugins = 'elementspath,save,image,flash,iframe,link,smiley,tabletools,find,pagebreak,templates,about,maximize,showblocks,newpage,language';
config.removeButtons = 'Copy,Cut,Paste,Undo,Redo,Print,Form,TextField,Textarea,Button,SelectAll,NumberedList,BulletedList,CreateDiv,Table,PasteText,PasteFromWord,Select,HiddenField';