uses
  ComObj;

const
  CLSID_TaskbarList: TGUID = '{56FDF344-FD6D-11d0-958A-006097C9A090}';
type
  ITaskbarList = interface
    ['{56FDF342-FD6D-11d0-958A-006097C9A090}']
       function HrInit: HResult; stdcall;
       function AddTab(hwnd: Cardinal): HResult; stdcall;
       function DeleteTab(hwnd: Cardinal): HResult; stdcall;
       function ActivateTab(hwnd: Cardinal): HResult; stdcall;
       function SetActiveAlt(hwnd: Cardinal): HResult; stdcall;
  end;

implementation

procedure TForm1.Button1Click(Sender: TObject);
const
  CLSID_TaskBarList: TGUID ='{56FDF344-FD6D-11D0-958A-006097C9A090}';
  IID_ITaskBarList: TGUID ='{56FDF342-FD6D-11D0-958A-006097C9A090}';
var
  FTaskbarList: ITaskBarList;
  Wnd: hWnd;
begin
  Wnd := FindWindow('IEFrame',nil);
  if (Wnd <> 0) then
  begin
     FTaskbarList := CreateComObject(CLSID_TaskbarList) as ITaskbarList;
     FTaskbarList.HrInit;
     FTaskbarList.HrInit;
     FTaskbarList.DeleteTab(Wnd);
  end;
end;