Summary:
The Framework is inconsistent in how listeners are removed in certain classes. This issue has been discussed in https://github.com/facebook/react-native/issues/6493.
For example,
**DeviceEventEmitter**
```javascript
/* Current */
this.keyboardHideObserver = DeviceEventEmitter.addListener('keyboardWillHide', this.keyboardWillHide);
this.keyboardHideObserver.remove();
/* Expected (maybe in addition to the current API) */
DeviceEventEmitter.addListener('keyboardWillHide', this.keyboardWillHide);
DeviceEventEmitter.removeListener('keyboardWillHide', this.keyboardWillHide);
```
**AppStateIOS**
```javascript
AppStateIOS.addEventListener('change', this.handleAppStateChange);
AppStateIOS.removeEventListener('change', this.handleAppStateChange);
```
The API should be consistent, and preferably should allow both ways of removing the listeners.
Currently, developers who tried to use the second way of removing the listeners get an error for function not found. Due to the lack of documenta
Closes https://github.com/facebook/react-native/pull/6884
Differential Revision: D3341235
Pulled By: nicklockwood
fbshipit-source-id: 87431e8b667f46ad002d4a6e3ca07cbc1e6b4007
0e8c3ff463