[promises] remove kPending check in RejectPromise

RejectPromise is always called on a pending promise making this a redundant check.

BUG=v8:5343

Review-Url: https://codereview.chromium.org/2446113007
Cr-Commit-Position: refs/heads/master@{#40591}

src/js/promise.js

@@ -302,19 +302,16 @@ function ResolvePromise(promise, resolution) {
 // ES#sec-rejectpromise
 // RejectPromise ( promise, reason )
 function RejectPromise(promise, reason, debugEvent) {
-  // Check promise status to confirm that this reject has an effect.
   // Call runtime for callbacks to the debugger or for unhandled reject.
   // The debugEvent parameter sets whether a debug ExceptionEvent should
   // be triggered. It should be set to false when forwarding a rejection
   // rather than creating a new one.
-  if (GET_PRIVATE(promise, promiseStateSymbol) === kPending) {
   // This check is redundant with checks in the runtime, but it may help
   // avoid unnecessary runtime calls.
   if ((debugEvent && DEBUG_IS_ACTIVE) ||
       !HAS_DEFINED_PRIVATE(promise, promiseHasHandlerSymbol)) {
     %PromiseRejectEvent(promise, reason, debugEvent);
   }
-  }
   %PromiseFulfill(promise, kRejected, reason, promiseRejectReactionsSymbol)
   PromiseSet(promise, kRejected, reason);
 }