Revert "http: check if incoming parser has already been freed"

This reverts commit 9f4c3b0.

Author: isaacs

lib/http.js

@@ -420,7 +420,7 @@ IncomingMessage.prototype._dump = function() {
     return;
 
   this._dumped = true;
-  if (this.socket.parser) this.socket.parser.incoming = null;
+  this.socket.parser.incoming = null;
   this.push(null);
   readStart(this.socket);
 };