Make from __future__ import annotations the default in Python 3.9

Author: ambv

pep-0563.rst

@@ -280,13 +280,7 @@ Deprecation policy
 Starting with Python 3.7, a ``__future__`` import is required to use the
 described functionality. No warnings are raised.
 
-In Python 3.8 a ``PendingDeprecationWarning`` is raised by the
-compiler in the presence of type annotations in modules without the
-``__future__`` import.
-
-Starting with Python 3.9 the warning becomes a ``DeprecationWarning``.
-
-In Python 4.0 this will become the default behavior. Use of annotations
+In Python 3.9 this will become the default behavior. Use of annotations
 incompatible with this PEP is no longer supported.