bpo-34687: Update asyncio doc for ProactorEventLoop (GH-9623)

Since ProactorEventLoop is now the default in 3.8, remove examples
using it explicitly on Windows.





https://bugs.python.org/issue34687

Author: vstinner

Doc/library/asyncio-eventloop.rst

@@ -1432,15 +1432,6 @@ on all platforms.
 
    Availability: Windows.
 
-   An example how to use :class:`ProactorEventLoop` on Windows::
-
-        import asyncio
-        import sys
-
-        if sys.platform == 'win32':
-            loop = asyncio.ProactorEventLoop()
-            asyncio.set_event_loop(loop)
-
    .. seealso::
 
       `MSDN documentation on I/O Completion Ports

Doc/library/asyncio-protocol.rst

@@ -1030,10 +1030,6 @@ The subprocess is created by th :meth:`loop.subprocess_exec` method::
         data = bytes(protocol.output)
         return data.decode('ascii').rstrip()
 
-    if sys.platform == "win32":
-        asyncio.set_event_loop_policy(
-            asyncio.WindowsProactorEventLoopPolicy())
-
     date = asyncio.run(get_date())
     print(f"Current date: {date}")
 

Doc/library/asyncio-subprocess.rst

@@ -344,10 +344,6 @@ function::
         await proc.wait()
         return line
 
-    if sys.platform == "win32":
-        asyncio.set_event_loop_policy(
-            asyncio.WindowsProactorEventLoopPolicy())
-
     date = asyncio.run(get_date())
     print(f"Current date: {date}")