lib: add note about removing node:sys module

PR-URL: nodejs#54743
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/sys.js

@@ -24,6 +24,8 @@
 // The sys module was renamed to 'util'. This shim remains to keep old programs
 // working. `sys` is deprecated and shouldn't be used.
 
+// Note to maintainers: Although this module has been deprecated for a while
+// we do not plan to remove it. See: https://github.com/nodejs/node/pull/35407#issuecomment-700693439
 module.exports = require('util');
 process.emitWarning('sys is deprecated. Use util instead.',
                     'DeprecationWarning', 'DEP0025');