migrate to expo-linear-gradient (#3420)

* replace packages

* rm useless alias from webpack config

* fix accidental double commit

* replace all usages

webpack.config.js

@@ -20,7 +20,6 @@ module.exports = async function (env, argv) {
   let config = await createExpoWebpackConfigAsync(env, argv)
   config = withAlias(config, {
     'react-native$': 'react-native-web',
-    'react-native-linear-gradient': 'react-native-web-linear-gradient',
     'react-native-webview': 'react-native-web-webview',
   })
   config.module.rules = [