NSKeyValuePopPendingNotificationLocal Crash on iOS 13 and 14

It is caused by FirebasePerformance v3.3.1 and XCode 12. Use 'FirebasePerformance', '3.3.0' should solve the problem.

After setting FirebasePerformance to v3.3.0, we did not see any NSKeyValuePopPendingNotificationLocal, AFURLSessionManager, NSKVODeallocate, CFDictionaryGetValue, NSKeyValueWillChange, [NSObject(NSKeyValueObservingPrivate) _changeValueForKeys:count:maybeOldValuesDict:maybeNewValuesDict:usingBlock:]... crashes anymore.

The crash-free percentage is recovered from 95% to 99.9%.