doc: remove experimental abortcontroller flag

PR-URL: https://github.com/nodejs/node/pull/38968
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

doc/api/cli.md

@@ -253,21 +253,6 @@ effort to report stack traces relative to the original source file.
 Overriding `Error.prepareStackTrace` prevents `--enable-source-maps` from
 modifying the stack trace.
 
-### `--experimental-abortcontroller`
-
-<!-- YAML
-added:
-  - v15.0.0
-  - v14.17.0
-changes:
-  - version: v15.0.0
-    pr-url: https://github.com/nodejs/node/pull/33527
-    description: --experimental-abortcontroller is no longer required.
--->
-
-`AbortController` and `AbortSignal` support is enabled by default.
-Use of this command-line flag is no longer required.
-
 ### `--experimental-import-meta-resolve`
 
 <!-- YAML