doc: change encoding to decoding

As per the example, `querystring.parse` actually does URL decoding, not
encoding.

PR-URL: nodejs#15706
Reviewed-By: Timothy Gu <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>

doc/api/deprecations.md

@@ -675,7 +675,7 @@ querystring.parse(str, '\n', '=');
 ```
 
 *Note*: This function is not completely equivalent to `querystring.parse()`. One
-difference is that `querystring.parse()` does url encoding:
+difference is that `querystring.parse()` does url decoding:
 
 ```sh
 > querystring.parse('%E5%A5%BD=1', '\n', '=');