fix(util-user-agent-browser): react native metadata (#2210)

Fix the react native entry point. Need to use the entry point
pattern in react-native field of package.json, instead of replace
pattern in clients. Because the later one isn't applicable to
entry point file like index.js

Author: AllanZhengYP

Diff for: packages/util-user-agent-browser/package.json

@@ -17,9 +17,7 @@
     "url": "https://aws.amazon.com/javascript/"
   },
   "license": "Apache-2.0",
-  "react-native": {
-    "./index": "./index.native"
-  },
+  "react-native": "dist/es/index.native.js",
   "dependencies": {
     "@aws-sdk/types": "3.10.0",
     "bowser": "^2.11.0",