Remove antiquated \since lines in docs.

They aren't useful in the case of QtMultimedia{Kit}

Change-Id: If1b0b6625763c85907fb05beb9c440046472ddef
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/imports/multimedia/qdeclarativecamera.cpp

@@ -70,7 +70,6 @@ void QDeclarativeCamera::_q_updateState(QCamera::State state)
 
 /*!
     \qmlclass Camera QDeclarativeCamera
-    \since 4.7
     \brief The Camera element allows you to add camera viewfinder to a scene.
     \ingroup qml-multimedia
     \inherits Item