doc: remove personal pronoun from worker_threads

Per the Style Guide, remove the use of the personal pronoun _you_ from
the formal API documentation for `worker_threads`.

PR-URL: #23347
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

Author: Trott

doc/api/worker_threads.md

@@ -154,8 +154,8 @@ added: v10.5.0
 -->
 
 Disables further sending of messages on either side of the connection.
-This method can be called once you know that no further communication
-will happen over this `MessagePort`.
+This method can be called when no further communication will happen over this
+`MessagePort`.
 
 ### port.postMessage(value[, transferList])
 <!-- YAML
@@ -436,9 +436,9 @@ to have completed.
 
 **Warning**: Currently, not all code in the internals of Node.js is prepared to
 expect termination at arbitrary points in time and may crash if it encounters
-that condition. Consequently, you should currently only call `.terminate()` if
-it is known that the Worker thread is not accessing Node.js core modules other
-than what is exposed in the `worker` module.
+that condition. Consequently, only call `.terminate()` if it is known that the
+Worker thread is not accessing Node.js core modules other than what is exposed
+in the `worker` module.
 
 ### worker.threadId
 <!-- YAML