[Docs] Revert doc change about final class generation

[MrYamous]

While reading documentation about this bundle, i've found this in configuration section

By default, MakerBundle will generate all of your classes with the final PHP keyword except for doctrine entities. Set this to false to override this behavior for all maker commands.

I think this new configuration is a good idea, but in current state, this sentence looks wrong to me. Some classes such WebhookConsumer or RequestParser are always generated as final and some others, TwigExtension or EventSubscriber are never

This could lead to a kind of strange state with this configuration available without being functional everywhere (as is already the case) but at the moment I feel like the documentation is misleading on this specific point