Use opaque_keys w/ model vars not parsing of url

to generate url.
LMS-11209

lms/templates/courseware/xqa_interface.html

@@ -16,15 +16,7 @@ function setup_debug(element_id, edit_link, staff_context){
             var username = $("#" + element_id + "_history_student_username").val();
             var location = $("#" + element_id + "_history_location").val();
 
-			// This is a ridiculous way to get the course_id, but I'm not sure
-			// how to do it sensibly from within the staff debug code. 
-			// staff_problem_info.html is rendered through a wrapper to get_html
-			// that's injected by the code that adds the histogram -- it's all 
-			// kinda bizarre, and it remains awkward to simply ask "what course
-			// is this problem being shown in the context of."
-			var path_parts = window.location.pathname.split('/');
-			var course_id = path_parts[2] + "/" + path_parts[3] + "/" + path_parts[4];
-			$("#" + element_id + "_history_text").load('/courses/' + course_id + 
+            $("#" + element_id + "_history_text").load('/courses/' + "${unicode(course.id)}" + 
                 "/submission_history/" + username + "/" + location);
             return false;
         }