[SecurityBundle] Add missing removed config options to upgrade guide

Author: W0rma

CHANGELOG.md

@@ -5,7 +5,9 @@ CHANGELOG
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  * Enabling SecurityBundle and not configuring it is not allowed
- * Remove configuration options `enable_authenticator_manager`, `csrf_token_generator` and `require_previous_session`
+ * Remove the `enable_authenticator_manager` config option
+ * Remove the `security.firewalls.logout.csrf_token_generator` config option, use `security.firewalls.logout.csrf_token_manager` instead
+ * Remove the `require_previous_session` config option from authenticators
 
 6.4
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