bpo-38203: faulthandler.dump_traceback_later() is always available (GH-16260)

dump_traceback_later() and cancel_dump_traceback_later() functions of
the faulthandler module are always available since Python 3.7.

Author: vstinner

Doc/library/faulthandler.rst

@@ -100,8 +100,10 @@ Dumping the tracebacks after a timeout
    :func:`cancel_dump_traceback_later` is called: see :ref:`issue with file
    descriptors <faulthandler-fd>`.
 
-   This function is implemented using a watchdog thread and therefore is not
-   available if Python is compiled with threads disabled.
+   This function is implemented using a watchdog thread.
+
+   .. versionchanged:: 3.7
+      This function is now always available.
 
    .. versionchanged:: 3.5
       Added support for passing file descriptor to this function.