doc,stream: remove wrong remark on readable.read

The returned chunk is *never* longer than `size`.

PR-URL: #15014
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/stream.md

@@ -863,7 +863,7 @@ in object mode.
 The optional `size` argument specifies a specific number of bytes to read. If
 `size` bytes are not available to be read, `null` will be returned *unless*
 the stream has ended, in which case all of the data remaining in the internal
-buffer will be returned (*even if it exceeds `size` bytes*).
+buffer will be returned.
 
 If the `size` argument is not specified, all of the data contained in the
 internal buffer will be returned.