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: facebook/react-native#22083

Differential Revision: D12929443

Pulled By: TheSavior

fbshipit-source-id: d42b0be3db745e445447e65df3b78b61f53e4229

SliderExample.js

@@ -69,10 +69,6 @@ class SlidingCompleteExample extends React.Component<
 }
 
 const styles = StyleSheet.create({
-  slider: {
-    height: 10,
-    margin: 10,
-  },
   text: {
     fontSize: 14,
     textAlign: 'center',