Use "= default" rather than empty bodies for ctors and dtors

Change-Id: Idef0ebaa0074e1e4b6b74d20bd6c70cb22a04f93
Reviewed-by: Maximilian Goldstein <max.goldstein@qt.io>

examples/quick/scenegraph/customgeometry/beziercurve.cpp

@@ -67,9 +67,7 @@ BezierCurve::BezierCurve(QQuickItem *parent)
 //! [1]
 
 //! [2]
-BezierCurve::~BezierCurve()
-{
-}
+BezierCurve::~BezierCurve() = default;
 //! [2]
 
 //! [3]

src/qml/qml/qqmlengine.cpp

@@ -823,13 +823,8 @@ void QQmlData::flushPendingBindingImpl(QQmlPropertyIndex index)
                             QQmlPropertyData::DontRemoveBinding);
 }
 
-QQmlData::DeferredData::DeferredData()
-{
-}
-
-QQmlData::DeferredData::~DeferredData()
-{
-}
+QQmlData::DeferredData::DeferredData() = default;
+QQmlData::DeferredData::~DeferredData() = default;
 
 bool QQmlEnginePrivate::baseModulesUninitialized = true;
 void QQmlEnginePrivate::init()