WelcomeMode: Remove unused code

The "platform" function is not used in QML, so let's remove it. In case
it will be needed at some point in time, better use Qt.platform

Change-Id: Ie9cecf8f2953934fbe8b0bb16f2267975af30fd0
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

src/plugins/welcome/welcomeplugin.cpp

@@ -84,8 +84,6 @@ public:
     void initPlugins();
     int activePlugin() const { return m_activePlugin; }
 
-    Q_SCRIPTABLE QString platform() const;
-
 //    bool eventFilter(QObject *, QEvent *);
 
 public slots:
@@ -273,17 +271,6 @@ void WelcomeMode::initPlugins()
             QUrl::fromLocalFile(path));
 }
 
-QString WelcomeMode::platform() const
-{
-    switch (HostOsInfo::hostOs()) {
-    case OsTypeWindows: return QLatin1String("windows");
-    case OsTypeMac: return QLatin1String("mac");
-    case OsTypeLinux: return QLatin1String("linux");
-    case OsTypeOtherUnix: return QLatin1String("unix");
-    default: return QLatin1String("other");
-    }
-}
-
 void WelcomeMode::welcomePluginAdded(QObject *obj)
 {
     QHash<Utils::IWelcomePage::Id, Utils::IWelcomePage*> pluginHash;