Bug 1765822: Do not assert but just bail out on missing event target in nsTimerImpl::InitCommon. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D144540

xpcom/threads/nsTimerImpl.cpp

@@ -394,7 +394,6 @@ nsresult nsTimerImpl::InitCommon(const TimeDuration& aDelay, uint32_t aType,
                                  Callback&& newCallback,
                                  const MutexAutoLock& aProofOfLock) {
   if (!mEventTarget) {
-    NS_ERROR("mEventTarget is NULL");
     return NS_ERROR_NOT_INITIALIZED;
   }