[promises] Remove extra PromiseInit in InternalPromiseThen

R=adamk@chromium.org, caitp@igalia.com
BUG=v8:5343

Review-Url: https://codereview.chromium.org/2603033002
Cr-Commit-Position: refs/heads/master@{#41995}

src/builtins/builtins-promise.cc

@@ -225,7 +225,6 @@ Node* PromiseBuiltinsAssembler::InternalPromiseThen(Node* context,
   Bind(&fast_promise_capability);
   {
     Node* const deferred_promise = AllocateAndInitPromise(context, promise);
-    PromiseInit(deferred_promise);
     var_deferred_promise.Bind(deferred_promise);
     var_deferred_on_resolve.Bind(UndefinedConstant());
     var_deferred_on_reject.Bind(UndefinedConstant());