Remove babel plugins related to async await

.babelrc

@@ -2,9 +2,5 @@
   "presets": [
     "es2015",
     "es2017"
-  ],
-  "plugins": [
-    "transform-async-to-generator",
-    "transform-regenerator"
   ]
 }

index.js

@@ -1,5 +1,3 @@
-require("babel-polyfill");
-
 const api = require("./lib/api");
 const auth = require("./lib/auth");
 const broadcast = require("./lib/broadcast");

package.json

@@ -33,7 +33,6 @@
   },
   "homepage": "https://github.com/steemit/steem-js#readme",
   "dependencies": {
-    "babel-polyfill": "^6.23.0",
     "bigi": "^1.4.2",
     "bluebird": "^3.4.6",
     "browserify-aes": "^1.0.6",
@@ -54,8 +53,7 @@
     "babel-cli": "^6.16.0",
     "babel-eslint": "^7.1.1",
     "babel-loader": "^6.2.5",
-    "babel-plugin-transform-async-to-generator": "^6.24.1",
-    "babel-plugin-transform-regenerator": "^6.24.1",
+    "babel-polyfill": "^6.23.0",
     "babel-preset-es2015": "^6.16.0",
     "babel-preset-es2017": "^6.16.0",
     "babel-register": "^6.14.0",
@@ -77,4 +75,4 @@
     "Nilesh Suthar (https://github.com/nil1511)",
     "Pedro Tacla Yamada (https://github.com/yamadapc)"
   ]
-}
+}

src/browser.js

@@ -1,5 +1,3 @@
-require("babel-polyfill");
-
 const api = require("./api");
 const auth = require("./auth");
 const broadcast = require("./broadcast");