doc: remove unused link reference

PR-URL: #17510
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>

Author: apapirovski

doc/api/child_process.md

@@ -1360,7 +1360,6 @@ unavailable.
 
 [`'error'`]: #child_process_event_error
 [`'exit'`]: #child_process_event_exit
-[`'message'`]: #child_process_event_message
 [`ChildProcess`]: #child_process_child_process
 [`Error`]: errors.html#errors_class_error
 [`EventEmitter`]: events.html#events_class_eventemitter