[change] Remove ART export

Anticipate the removal of ART from React Native core:
https://github.com/facebook/react-native/issues/23313

Simplifies dependencies and builds for web apps.

Close #1251

packages/examples/src/RNTester/RNTesterList.web.js

@@ -20,10 +20,6 @@ const ComponentExamples: Array<RNTesterExample> = [
     key: 'ActivityIndicatorExample',
     module: require('./ActivityIndicatorExample')
   },
-  {
-    key: 'ARTExample',
-    module: require('./ARTExample')
-  },
   {
     key: 'ButtonExample',
     module: require('./ButtonExample')