http: docs-only deprecation of res.writeHeader()

Doc-only deprecation of the undocumented res.writeHeader() API.
Also makes res.writeHeader an alias of res.writeHead since the
previous implementation simply deferred to that method.

PR-URL: https://github.com/nodejs/node/pull/11355
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

lib/_http_server.js

@@ -231,9 +231,8 @@ function writeHead(statusCode, reason, obj) {
   this._storeHeader(statusLine, headers);
 }
 
-ServerResponse.prototype.writeHeader = function writeHeader() {
-  this.writeHead.apply(this, arguments);
-};
+// Docs-only deprecated: DEP0063
+ServerResponse.prototype.writeHeader = ServerResponse.prototype.writeHead;
 
 
 function Server(requestListener) {