Fix arrow navigation in TreeWidget

Closes FreeCAD#10488. This commit removes the code fragment that "swallowed"
the key press events.

src/Gui/Tree.cpp

@@ -1682,22 +1682,7 @@ void TreeWidget::keyPressEvent(QKeyEvent* event)
             return;
         }
     }
-    else if (event->key() == Qt::Key_Left) {
-        auto index = currentIndex();
-        if (index.column() == 1) {
-            setCurrentIndex(model()->index(index.row(), 0, index.parent()));
-            event->accept();
-            return;
-        }
-    }
-    else if (event->key() == Qt::Key_Right) {
-        auto index = currentIndex();
-        if (index.column() == 0) {
-            setCurrentIndex(model()->index(index.row(), 1, index.parent()));
-            event->accept();
-            return;
-        }
-    }
+
     QTreeWidget::keyPressEvent(event);
 }