message: Copied over dealloc
  Not sure it's necessary because it's removed in the child unmount but think it's being extra safe. Should maybe put it in prepareForRecycle?!
diff: @@ -163,6 +163,11 @@ using namespace facebook::react;
  }
  }
  +- (void)dealloc
  +{
  + [_reactSubview removeObserver:self forKeyPath:@"hidden"];
  +}
  +
  #pragma mark - RCTComponentViewProtocol
  - (void)mountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
  