fix review finding

Author: sbueringer

docs/book/src/tasks/experimental-features/runtime-sdk/implement-extensions.md

@@ -286,8 +286,6 @@ considerations apply:
 - It is the responsibility of Cluster API components to surface Runtime Extension errors using conditions.
 - Operations will be retried with an exponential backoff or whenever the state of a Cluster changes (we are going to rely
   on controller runtime exponential backoff/watches).
-- If the operation is defined as "blocking", the error is going to block a lifecycle transition, e.g. returning a non-zero 
-  `retryAfterSeconds` on a Runtime Extension for the `BeforeClusterUpgrade` hook is going to block the Cluster upgrade.
 - If there is more than one Runtime Extension registered for the same Runtime Hook and at least one of them fails,
   all the registered Runtime Extension will be retried. See [Idempotence](#idempotence)