PEP-654: simplify traverse() example (#1844)

We don't need to pass the cause and context from the root. The ones for the leaf are on the leaf exception itself.

pep-0654.rst

@@ -330,20 +330,18 @@ calling ``traverse(eg)``, where ``traverse`` is defined as follows:
 
 .. code-block::
 
-    def traverse(exc, tbs=None, cause=None, context=None):
+    def traverse(exc, tbs=None):
         if tbs is None:
             tbs = []
-            cause = exc.__cause__
-            context = exc.__context__
 
         tbs.append(exc.__traceback__)
         if isinstance(exc, ExceptionGroup):
             for e in exc.errors:
-                traverse(e, tbs, cause, context)
+                traverse(e, tbs)
         else:
             # exc is a leaf exception and its traceback
             # is the concatenation of the traceback in tbs
-            process_leaf(exc, tbs, cause, context)
+            process_leaf(exc, tbs)
         tbs.pop()