Drop the use of es6-promise as it's covered by babelrc and corejs (#2788)

Author: pcorpet

package.json

@@ -57,7 +57,6 @@
     "css-loader": "4.3.0",
     "date-fns": "2.16.1",
     "detect-browser": "5.2.0",
-    "es6-promise": "4.2.8",
     "es6-set-proptypes": "1.0.0",
     "eslint": "7.18.0",
     "eslint-import-resolver-typescript": "2.3.0",

webpack.config.js

@@ -1,5 +1,4 @@
 'use strict'
-require('es6-promise').polyfill()
 
 var path = require('path')
 var args = require('minimist')(process.argv.slice(2))