WinRT: fix QLibrary::isLibrary() due to incomplete #if statement

Q_OS_WINRT was missing in the Windows-condition.
Condition was simplified through use of Q_OS_WIN.

Change-Id: I1a49d2d9c413dc2156930b6915e1675abcdde36f
Reviewed-by: Oliver Wolff <oliver.wolff@theqtcompany.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>

src/corelib/plugin/qlibrary.cpp

@@ -606,7 +606,7 @@ bool QLibraryPrivate::loadPlugin()
  */
 bool QLibrary::isLibrary(const QString &fileName)
 {
-#if defined(Q_OS_WIN32) || defined(Q_OS_WINCE)
+#if defined(Q_OS_WIN)
     return fileName.endsWith(QLatin1String(".dll"), Qt::CaseInsensitive);
 #else
     QString completeSuffix = QFileInfo(fileName).completeSuffix();