Removing the call to observeValueForKeyPath:ofObject:change:context: on super from RCTVideo.

If the super class is not actually observing the key, the app will crash. Checking to see if
the super class responds to this selector doesn't solve this issue.

react-native-video github issue: https://github.com/react-native-community/react-native-video/issues/1515

Discussion about this particular problem: https://stackoverflow.com/questions/6574714/whats-wrong-with-this-observevalueforkeypathofobjectchangecontext-implement