Remove observer in setSrc if the source changes, but the view hasn't been removed from superview

Before: observer removes only in removeFromSuperview, but adds in setSrc – multiple setSrc would add multiple observers and one removeFromSuperview would remove only one observer. Now: Every addObserver in setSrc is balanced by removeObserver also in setSrc

RCTVideo.m

@@ -225,6 +225,11 @@ static NSString *const playbackRate = @"rate";
 
   _player = [AVPlayer playerWithPlayerItem:_playerItem];
   _player.actionAtItemEnd = AVPlayerActionAtItemEndNone;
+    
+  if (_playbackRateObserverRegistered) {
+    [_player removeObserver:self forKeyPath:playbackRate];
+    _playbackRateObserverRegistered = NO;
+  }
   [_player addObserver:self forKeyPath:playbackRate options:0 context:nil];
   _playbackRateObserverRegistered = YES;