traceback2 adds traceback for python2. Rather than depend on traceback2, we're
python3 only so just use traceback.
This caused breakage in oe-selftest -j which uses testtools on the autobuilder
using buildtools-tarball.

Upstream-Status: Inappropriate [Our recipe is python3 specific]
(Once py2 is EOL upstream probably could/should take this)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Index: testtools-2.3.0/testtools/content.py
===================================================================
--- testtools-2.3.0.orig/testtools/content.py
+++ testtools-2.3.0/testtools/content.py
@@ -19,8 +19,7 @@ import os
 import sys
 
 from extras import try_import
-# To let setup.py work, make this a conditional import.
-traceback = try_import('traceback2')
+import traceback
 
 from testtools.compat import (
     _b,