ErrorController: Stop logging the useless exception when c.user unset

The exception isn't a trace from the current point, but from the last
handled exception. This is not useful and is spamming up the logs.

r2/r2/controllers/error.py

@@ -217,7 +217,6 @@ def GET_document(self):
                 # somehow requests are getting here with c.user unset
                 c.user_is_loggedin = False
                 c.user = UnloggedUser(browser_langs=None)
-                g.log.exception("ErrorController.GET_document unset c.user")
 
             if srname:
                 c.site = Subreddit._by_name(srname)