bpo-42482: remove reference to exc_traceback from TracebackException (GH-23531)



diff --git a/Lib/traceback.py b/Lib/traceback.py
index d2d93c8..457d925 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -510,7 +510,6 @@ def __init__(self, exc_type, exc_value, exc_traceback, *, limit=None,
                 _seen=_seen)
         else:
             context = None
-        self.exc_traceback = exc_traceback
         self.__cause__ = cause
         self.__context__ = context
         self.__suppress_context__ = \
@@ -627,7 +626,7 @@ def format(self, *, chain=True):
                 not self.__suppress_context__):
                 yield from self.__context__.format(chain=chain)
                 yield _context_message
-        if self.exc_traceback is not None:
+        if self.stack:
             yield 'Traceback (most recent call last):\n'
-        yield from self.stack.format()
+            yield from self.stack.format()
         yield from self.format_exception_only()