[libcalamares] Avoid static destructor

- The static destructor issues a warning on exit:
       QBasicTimer::start: QBasicTimer can only be used with threads
       started with QThread
   so instead, heap-allocate the model. This leaks memory, but
   it's a singleton *and* we're exiting anyway.

src/libcalamares/locale/LabelModel.cpp

@@ -125,8 +125,8 @@ LabelModel::find( const QString& countryCode ) const
 
 LabelModel* availableTranslations()
 {
-    static LabelModel model( QString( CALAMARES_TRANSLATION_LANGUAGES ).split( ';') );
-    return &model;
+    static LabelModel* model = new LabelModel( QString( CALAMARES_TRANSLATION_LANGUAGES ).split( ';') );
+    return model;
 }
 
 }