util: clear debugstacktrace call

During the renaming of datestr, it seems that I have forget a debugstacktrace
in util.py. Remove it.

Differential Revision: https://phab.mercurial-scm.org/D2838

mercurial/util.py

@@ -4053,7 +4053,6 b' def datestr(*args, **kwargs):'
     msg = ("'util.datestr' is deprecated, "
            "use 'utils.dateutil.datestr'")
     nouideprecwarn(msg, "4.6")
-    debugstacktrace()
     return dateutil.datestr(*args, **kwargs)
 
 def shortdate(*args, **kwargs):