doc: remove unused functions from example of streamConsumers.text

json, blob, and buffer are imported, but these functions are not
used for example of `streamConsumers.text`.

PR-URL: #46581
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: deokjinkim

doc/api/webstreams.md

@@ -1613,7 +1613,7 @@ added: v16.7.0
   UTF-8 encoded string.
 
 ```mjs
-import { json, text, blob, buffer } from 'node:stream/consumers';
+import { text } from 'node:stream/consumers';
 import { Readable } from 'node:stream';
 
 const readable = Readable.from('Hello world from consumers!');