Professional User Interface Suite, Copyright FOSS Software Inc. Help Published with Permission.

To remove the right-most button in the toolbar, which is also known as "a toolbar option button" or "chevron button", override the CExtToolControlBar::OnCreateBarRightBtn() method and just return NULL:

class CMyToolControlBar : public CExtToolControlBar
{
    virtual CExtBarContentExpandButton * OnCreateBarRightBtn(){ 
      return NULL; 
    }
};