Fix Clang warning about copy elision

Found by Clang 3.7:

qcommandlineoption.cpp:287:12: error: moving a local object in a return statement prevents copy elision [-Werror,-Wpessimizing-move]

Change-Id: I7de033f80b0e4431b7f1ffff13f97fb480001d36
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/tools/qcommandlineoption.cpp

@@ -284,7 +284,7 @@ QStringList QCommandLineOptionPrivate::removeInvalidNames(QStringList nameList)
     else
         nameList.erase(std::remove_if(nameList.begin(), nameList.end(), IsInvalidName()),
                        nameList.end());
-    return qMove(nameList);
+    return nameList;
 }
 
 /*!