Revert "Tidy up render_modal_workflow"

This reverts commit 1505e0b789.

wagtail/wagtailadmin/modal_workflow.py

@@ -6,18 +6,20 @@ from wagtail.utils.compat import render_to_string
 
 
 def render_modal_workflow(request, html_template, js_template, template_vars=None):
-    """
+    """"
     Render a response consisting of an HTML chunk and a JS onload chunk
     in the format required by the modal-workflow framework.
     """
-    response_keyvars = {}
+    response_keyvars = []
 
     if html_template:
         html = render_to_string(html_template, template_vars or {}, request=request)
-        response_keyvars['html'] = html
+        response_keyvars.append("'html': %s" % json.dumps(html))
 
     if js_template:
         js = render_to_string(js_template, template_vars or {}, request=request)
-        response_keyvars['onload'] = js
+        response_keyvars.append("'onload': %s" % js)
 
-    return HttpResponse(json.dumps(response_keyvars), content_type="application/json")
+    response_text = "{%s}" % ','.join(response_keyvars)
+
+    return HttpResponse(response_text, content_type="text/javascript")