Replace local copy of text-encoding with dependency

Removed copied source of the text-encoding library and added a regular
npm dependency instead.

Author: lutovich

package-lock.json

@@ -72,6 +72,7 @@
   },
   "dependencies": {
     "babel-runtime": "^6.26.0",
+    "text-encoding": "^0.6.4",
     "uri-js": "^4.2.1"
   }
 }