delete unused member variable (#43551)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/43551

changelog: [internal]

unused member variable. Let's remove it

Reviewed By: rubennorte

Differential Revision: D54754610

fbshipit-source-id: 0ed6a71314f25d00779312bd97d46875c2723e9a