Summary:
Use AndroidX in ReactAndroid/build.gradle, and remove androidx dependency from template and RNTester app because it's already exposed/exported from ReactAndroid.
[Android] [Changed] - Land AndroidX in gradle
Pull Request resolved: https://github.com/facebook/react-native/pull/24014
Differential Revision: D14508774
Pulled By: mdvacca
fbshipit-source-id: c96b97876571a5a7f2b400dd29188cfdf1f84a4c