Fix incorrect statement in QTreeWidgetItem docs.

Task-number: QTBUG-25598

Change-Id: Ib90578081d4e52877ce4842ebbc824ef74179341
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Refer to setDragEnabled in QLineEdit's detailed description.

It's currently not obvious how to drag text from a QLineEdit.

Task-number: QTBUG-22413

Change-Id: I5b92ce5c7425a1cb8ee6f401c685424eb9396592
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>