Replace set[Plain]Text(QString()) with clear()

...where applicable. Shorter, faster, more semantic.

Change-Id: Ifb1cf200f489f62a79e12c761e98a846992744dc
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/git/changeselectiondialog.cpp

@@ -244,7 +244,7 @@ void ChangeSelectionDialog::recalculateDetails()
 
     const QString ref = change();
     if (ref.isEmpty()) {
-        m_ui->detailsText->setPlainText(QString());
+        m_ui->detailsText->clear();
         return;
     }