http: remove unnecessary check

The value passed to `process.nextTick()` which is passed to the
callback is already a valid object, so the conditional will always
evaluate to true.

PR-URL: #5233
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_outgoing.js

@@ -489,8 +489,7 @@ function writeAfterEndNT(self, err, callback) {
 
 
 function connectionCorkNT(conn) {
-  if (conn)
-    conn.uncork();
+  conn.uncork();
 }