Remove __unicode__ method so that ``unicode(BaseException)`` succeeds.

Fixes bug #1551432.
diff --git a/Misc/NEWS b/Misc/NEWS
index b72e758..390ad73 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -19,6 +19,9 @@
 Core and builtins
 -----------------
 
+- Bug #1551432: Exceptions do not define an explicit __unicode__ method.  This
+  allows calling unicode() on exceptions classes directly to succeed.
+
 - Bug #1542051: Exceptions now correctly call PyObject_GC_UnTrack.
   Also make sure that every exception class has __module__ set to
   'exceptions'.