Remove deprecated getNode method

[gustavorodarte]

In react native 0.62 the method getNode is deprecated, and throw a warning when used.

https://github.com/facebook/react-native/commit/66e72bb4e00aafbcb9f450ed5db261d98f99f82a

[slorber]

Superseded by https://github.com/APSL/react-native-keyboard-aware-scroll-view/pull/484

• extractNativeRef is not an API to remove: I personally use it for another use-case where the wrapped scrollview is not an animated scroll view
• we should keep supporting RN <= 0.61 it possible