Update QtWebEngine version in module overview

Also remove QtQuick import. This one is not specific
for the module.

Change-Id: I0cdbb0f36823e109e0b4b93e65ae3de59aebd2b7
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>

src/webengine/doc/src/qtwebengine-qmlmodule.qdoc

@@ -33,8 +33,7 @@
     your .qml file:
 
     \badcode
-    import QtQuick 2.0
-    import QtWebEngine 1.1
+    import QtWebEngine 1.2
     \endcode
 
     To link against the module, add the following QT variable to your qmake .pro