Silence warnings about keyboard grab and size hint propagation

These two unimplemented functions often result in showing warnings
from the default implementations. This is not quite ideal since the
warning is useless for users and pollutes the standard output (which
f.ex. Creator captures as-is)

Change-Id: Ic05ff1590ed351738f0390a94ed5203a05664d4a
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -187,6 +187,9 @@ public:
     void setBackingStore(QWaylandShmBackingStore *backingStore) { mBackingStore = backingStore; }
     QWaylandShmBackingStore *backingStore() const { return mBackingStore; }
 
+    bool setKeyboardGrabEnabled(bool) Q_DECL_OVERRIDE { return false; }
+    void propagateSizeHints() Q_DECL_OVERRIDE { }
+
 public slots:
     void requestResize();