Revert "Workaround tornado+py38+windows compatibility issue (Same as i…

…python#456). Set eventloop policy to the old default while tornado is not compatible with the new one."

This reverts commit 06967ee.

ipykernel/ipkernel.py

@@ -57,25 +57,7 @@ def _user_ns_changed(self, name, old, new):
     _sys_raw_input = Any()
     _sys_eval_input = Any()
 
-    def _init_asyncio_patch(self):
-        if sys.platform.startswith("win") and sys.version_info >= (3, 8):
-            import asyncio
-            try:
-                from asyncio import (
-                    WindowsProactorEventLoopPolicy,
-                    WindowsSelectorEventLoopPolicy,
-                )
-            except ImportError:
-                pass
-                # not affected
-            else:
-                if type(asyncio.get_event_loop_policy()) is WindowsProactorEventLoopPolicy:
-                    # WindowsProactorEventLoopPolicy is not compatible with tornado 6
-                    # fallback to the pre-3.8 default of Selector
-                    asyncio.set_event_loop_policy(WindowsSelectorEventLoopPolicy())
-
     def __init__(self, **kwargs):
-        self._init_asyncio_patch()
         super(IPythonKernel, self).__init__(**kwargs)
 
         # Initialize the InteractiveShell subclass