doc: remove reference to resolved child_process v8 issue

The linked v8 issue is closed. The NodeJS half of that issue has also
been resolved. While there still may be issues related to
child_process spawn performance, they are not related to this v8 issue.

Refs: https://bugs.chromium.org/p/v8/issues/detail?id=7381
Refs: #48523
Refs: nodejs/performance#138
PR-URL: #51467
Reviewed-By: Keyhan Vakil <kvakil@sylph.kvakil.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: isker

doc/api/child_process.md

@@ -873,12 +873,6 @@ child registers an event handler for the [`'disconnect'`][] event
 or the [`'message'`][] event. This allows the child to exit
 normally without the process being held open by the open IPC channel._
 
-On Unix-like operating systems, the [`child_process.spawn()`][] method
-performs memory operations synchronously before decoupling the event loop
-from the child. Applications with a large memory footprint may find frequent
-[`child_process.spawn()`][] calls to be a bottleneck. For more information,
-see [V8 issue 7381](https://bugs.chromium.org/p/v8/issues/detail?id=7381).
-
 See also: [`child_process.exec()`][] and [`child_process.fork()`][].
 
 ## Synchronous process creation