doc: remove "this API is unstable" note for v8 serdes API

As #30234 marked this as stable I think this line
should be removed as well?

Refs: #30234
PR-URL: #30631
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

doc/api/v8.md

@@ -270,9 +270,6 @@ The serialization API provides means of serializing JavaScript values in a way
 that is compatible with the [HTML structured clone algorithm][].
 The format is backward-compatible (i.e. safe to store to disk).
 
-This API is under development, and changes (including incompatible
-changes to the API or wire format) may occur until this warning is removed.
-
 ### v8.serialize(value)
 <!-- YAML
 added: v8.0.0