Revert "THRIFT-2674 JavaScript: declare Accept: and Content-Type: in request"

This reverts commit 1e723d931e92652e4ccb1385709258759ae5bc54.
diff --git a/lib/js/src/thrift.js b/lib/js/src/thrift.js
index ada28ba..35f679c 100644
--- a/lib/js/src/thrift.js
+++ b/lib/js/src/thrift.js
@@ -327,11 +327,7 @@
         var xreq = this.getXmlHttpRequestObject();
 
         if (xreq.overrideMimeType) {
-            xreq.overrideMimeType('application/vnd.apache.thrift.json; charset=utf-8');
-        }
-        if (xreq.setRequestHeader) {
-            xreq.setRequestHeader('Accept', 'application/vnd.apache.thrift.json; charset=utf-8');
-            xreq.setRequestHeader('Content-Type', 'application/vnd.apache.thrift.json; charset=utf-8');
+            xreq.overrideMimeType('application/json');
         }
 
         if (callback) {
@@ -391,7 +387,7 @@
             data: postData,
             type: 'POST',
             cache: false,
-            contentType: 'application/vnd.apache.thrift.json; charset=utf-8',
+            contentType: 'application/json',
             dataType: 'text thrift',
             converters: {
                 'text thrift' : function(responseData) {