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

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

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

src/plugins/valgrind/callgrindtool.cpp

@@ -275,7 +275,7 @@ void CallgrindToolPrivate::doClear(bool clearParseData)
         m_filterProjectCosts->setChecked(false);
     m_proxyModel->setFilterBaseDir(QString());
     if (m_searchFilter)
-        m_searchFilter->setText(QString());
+        m_searchFilter->clear();
     m_proxyModel->setFilterFixedString(QString());
 }