remove legacy esnext module

Author: jeetiss

package.json

@@ -7,7 +7,6 @@
   "repository": "transitive-bullshit/react-modern-library-boilerplate",
   "main": "dist/index.js",
   "module": "dist/index.es.js",
-  "jsnext:main": "dist/index.es.js",
   "scripts": {
     "test": "CI=1 react-scripts test --env=jsdom",
     "build": "rollup -c",