Only consider startDragDistance for drag-n-drop tabs

The commit for https://phabricator.kde.org/D7451 changed DND to use
startDragDistance or startDragTime.  This can cause accidently DND of
tabs which creates new windows.

src/ViewContainerTabBar.cpp

@@ -83,8 +83,7 @@ void ViewContainerTabBar::mouseMoveEvent(QMouseEvent *event)
 {
     if (event->buttons() == Qt::LeftButton) {
         QPoint dragPos = _dragStart - event->pos();
-        if (dragPos.manhattanLength() > QApplication::startDragDistance()
-            || _mousePressTimer->elapsed() > QApplication::startDragTime()) {
+        if (dragPos.manhattanLength() > QApplication::startDragDistance()) {
             int tab = tabAt(_dragStart);
             if (tab != -1) {
                 emit initiateDrag(tab);