net: remove an unused internal module assertPort

A module `assertPort` in `lib/internal/net.js` is not used anymore.

Refs: #11667
PR-URL: #11812
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

lib/internal/net.js

@@ -1,7 +1,5 @@
 'use strict';
 
-module.exports = { isLegalPort, assertPort };
-
 // Check that the port number is not NaN when coerced to a number,
 // is an integer and that it falls within the legal range of port numbers.
 function isLegalPort(port) {
@@ -11,8 +9,6 @@ function isLegalPort(port) {
   return +port === (+port >>> 0) && port <= 0xFFFF;
 }
 
-
-function assertPort(port) {
-  if (typeof port !== 'undefined' && !isLegalPort(port))
-    throw new RangeError('"port" argument must be >= 0 and < 65536');
-}
+module.exports = {
+  isLegalPort
+};