doc: clarify removal of experimental API does not require a deprecation

PR-URL: #55746
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/documentation.md

@@ -44,6 +44,9 @@ The stability indexes are as follows:
 >   still occur in response to user feedback. We encourage user testing and
 >   feedback so that we can know that this feature is ready to be marked as
 >   stable.
+>
+> Experimental features leave the experimental status typically either by
+> graduating to stable, or are removed without a deprecation cycle.
 
 <!-- separator -->