Revert "Fixing overwrite Blob/File type as Content-Type in browser. (axios#1773)"

This reverts commit f3cc053.

Author: Gerhut

lib/adapters/xhr.js

@@ -18,13 +18,6 @@ module.exports = function xhrAdapter(config) {
       delete requestHeaders['Content-Type']; // Let the browser set it
     }
 
-    if (
-      (utils.isBlob(requestData) || utils.isFile(requestData)) &&
-      requestData.type
-    ) {
-      delete requestHeaders['Content-Type']; // Let the browser set it
-    }
-
     var request = new XMLHttpRequest();
 
     // HTTP basic authentication