winrt: avoid duplicate signal emit

emitChanged() will be invoked when the system notifies the application
about a clipboard change. Hence, there is no need to call it previously
and cause two signals on the same change to be emitted.

Change-Id: I99605c9a71054e0610006dbeaaa90c5fb2f46755
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

src/plugins/platforms/winrt/qwinrtclipboard.cpp

@@ -175,7 +175,6 @@ void QWinRTClipboard::setMimeData(QMimeData *data, QClipboard::Mode mode)
         return S_OK;
     });
     RETURN_VOID_IF_FAILED("Could not set clipboard text.");
-    emitChanged(mode);
 #else // Q_OS_WINPHONE
     QPlatformClipboard::setMimeData(data, mode);
 #endif // Q_OS_WINPHONE