Revert "Fixed isFormData predicate; (#4413)" (#4472)

This reverts commit 73e3bdb883.

lib/helpers/toFormData.js

@@ -1,7 +1,5 @@
 'use strict';
 
-var utils = require('../utils');
-
 function combinedKey(parentKey, elKey) {
   return parentKey + '.' + elKey;
 }
@@ -13,7 +11,7 @@ function buildFormData(formData, data, parentKey) {
     });
   } else if (
     typeof data === 'object' &&
-    !(utils.isFile(data) || data === null)
+    !(data instanceof File || data === null)
   ) {
     Object.keys(data).forEach(function buildObject(key) {
       buildFormData(
@@ -46,12 +44,10 @@ function buildFormData(formData, data, parentKey) {
  * type FormVal = FormDataNest | FormDataPrimitive
  *
  * @param {FormVal} data
- * @param {?Object} formData
  */
 
-module.exports = function getFormData(data, formData) {
-  // eslint-disable-next-line no-param-reassign
-  formData = formData || new FormData();
+module.exports = function getFormData(data) {
+  var formData = new FormData();
 
   buildFormData(formData, data);