cluster: remove obsolete todo

PR-URL: https://github.com/nodejs/node/pull/13734
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

lib/internal/cluster/shared_handle.js

@@ -11,9 +11,7 @@ function SharedHandle(key, address, port, addressType, fd, flags) {
   this.handle = null;
   this.errno = 0;
 
-  // FIXME(bnoordhuis) Polymorphic return type for lack of a better solution.
   var rval;
-
   if (addressType === 'udp4' || addressType === 'udp6')
     rval = dgram._createSocketHandle(address, port, addressType, fd, flags);
   else