docs: remove mention of PPE being in alpha (apify#1759)

Author: TC-MO

apify-api/openapi/paths/actor-runs/actor-runs@{runId}@charge.yaml

@@ -7,11 +7,6 @@ post:
     The event you are charging for must be one of the configured events in your Actor. If the Actor is not set up as pay per event, or if the event is not configured,
     the endpoint will return an error. The endpoint must be called from the Actor run itself, with the same API token that the run was started with.
 
-    :::note
-
-    Pay per events Actors are still in alpha. Please, reach out to us with any questions or feedback.
-
-    :::
   operationId: PostChargeRun
   parameters:
     - name: runId