Delete btoa polyfill

lib/helpers/btoa.js

@@ -1,36 +0,0 @@
-'use strict';
-
-// btoa polyfill for IE<10 courtesy https://github.com/davidchambers/Base64.js
-
-var chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
-
-function E() {
-  this.message = 'String contains an invalid character';
-}
-E.prototype = new Error;
-E.prototype.code = 5;
-E.prototype.name = 'InvalidCharacterError';
-
-function btoa(input) {
-  var str = String(input);
-  var output = '';
-  for (
-    // initialize result and counter
-    var block, charCode, idx = 0, map = chars;
-    // if the next str index does not exist:
-    //   change the mapping table to "="
-    //   check if d has no fractional digits
-    str.charAt(idx | 0) || (map = '=', idx % 1);
-    // "8 - idx % 1 * 8" generates the sequence 2, 4, 6, 8
-    output += map.charAt(63 & block >> 8 - idx % 1 * 8)
-  ) {
-    charCode = str.charCodeAt(idx += 3 / 4);
-    if (charCode > 0xFF) {
-      throw new E();
-    }
-    block = block << 8 | charCode;
-  }
-  return output;
-}
-
-module.exports = btoa;