Remove unused styles (#22083)

Summary:
Removes unused styles.

NOTE: Lint rule `react-native/no-unused-styles` not added because of custom lint rule internally at Facebook that does this.
Pull Request resolved: https://github.com/facebook/react-native/pull/22083

Differential Revision: D12929443

Pulled By: TheSavior

fbshipit-source-id: d42b0be3db745e445447e65df3b78b61f53e4229

RNTester/js/ListViewPagingExample.js

@@ -223,13 +223,6 @@ const styles = StyleSheet.create({
     color: 'white',
     paddingHorizontal: 8,
   },
-  rowText: {
-    color: '#888888',
-  },
-  thumbText: {
-    fontSize: 20,
-    color: '#888888',
-  },
   buttonContents: {
     flexDirection: 'row',
     justifyContent: 'center',