PushNotificationIOS.removeEventListener method signature requires unused handler Function

* * *
  This issue was originally created by @schumannd as facebook/react-native#23868.
  * * *

  https://github.com/facebook/react-native/blob/726d0012106316a40e36286f5eba0e881ef3bbba/Libraries/PushNotificationIOS/PushNotificationIOS.js#L236

This throws unhelpful flow errors. If this is an error, I can provide a PR removing this line.