Revert "Accept JSON from API"

This reverts commit f177720.

Author: Pat Patterson

forcetk.js

@@ -293,7 +293,6 @@ if (forcetk.Client === undefined) {
         var request = new XMLHttpRequest();
         request.open("POST", (this.proxyUrl !== null && ! this.visualforce) ? this.proxyUrl: url, this.asyncAjax);
 
-        request.setRequestHeader('Accept', 'application/json');
         request.setRequestHeader(this.authzHeader, "Bearer " + this.sessionId);
         request.setRequestHeader('X-User-Agent', 'salesforce-toolkit-rest-javascript/' + this.apiVersion);
         if (this.proxyUrl !== null && ! this.visualforce) {