PEP 828: Remove incorrect async yield from (#5114)

Author: graingert

peps/pep-0828.rst

@@ -357,7 +357,7 @@ to :meth:`~generator.close`.
 It's trivial for anyone who needs to delegate to a subgenerator to write
 the wrapper class to upgrade a synchronous :class:`~collections.abc.Iterable`
 or :class:`~collections.abc.Generator` to an
-async one before calling ``async yield from``.
+async one before calling ``yield from``.
 
 .. code-block:: python