Removing `@register_integration("asyncio")` and `def loop_asyncio(kernel):`

[NewUserHa]

In current versions of ipykernel, when you execute in jupyter, vscode jupyter,

%gui asyncio

then after a while, when you execute

import asyncio
asyncio.all_tasks()```

you will get and see like

{<Task pending name='Task-52016' coro=<_async_in_context.<locals>.run_in_context() running at D:\test\ipykernel\ipykernel\utils.py:60> wait_for=<Task pending name='Task-52017' coro=<Kernel.shell_main() running at D:\test\ipykernel\ipykernel\kernelbase.py:621> cb=[Task.task_wakeup()]> cb=[ZMQStream._run_callback.<locals>._log_error() at e:\.pixi\envs\default\Lib\site-packages\zmq\eventloop\zmqstream.py:563]>, 
<Task pending name='Task-5217' coro=<Kernel.shell_main() running at D:\test\ipykernel\ipykernel\kernelbase.py:621> cb=[Task.task_wakeup()]>}

It keeps increasing task count and it wastes your some cpu resource in the background. It's acually running these below codes, it just enters the function the return repeatedly, by self.io_loop.call_later(0.001, advance_eventloop) of enter_eventloop() in kernelbase.py.

ipykernel/ipykernel/eventloops.py

Lines 430 to 473 in 8816d02

	@register_integration("asyncio")
	def loop_asyncio(kernel):
	"""Start a kernel with asyncio event loop support."""
	import asyncio
	loop = asyncio.get_event_loop()
	# loop is already running (e.g. tornado 5), nothing left to do
	if loop.is_running():
	return
	if loop.is_closed():
	# main loop is closed, create a new one
	loop = asyncio.new_event_loop()
	asyncio.set_event_loop(loop)
	loop._should_close = False # type:ignore[attr-defined]
	# pause eventloop when there's an event on a zmq socket
	def process_stream_events(shell_stream):
	"""fall back to main loop when there's a socket event"""
	if shell_stream.flush(limit=1):
	loop.stop()
	shell_stream = get_shell_stream(kernel)
	notifier = partial(process_stream_events, shell_stream)
	loop.add_reader(shell_stream.getsockopt(zmq.FD), notifier)
	loop.call_soon(notifier)
	while True:
	error = None
	try:
	loop.run_forever()
	except KeyboardInterrupt:
	continue
	except Exception as e:
	error = e
	if loop._should_close: # type:ignore[attr-defined]
	loop.close()
	if error is not None:
	raise error
	break
	@loop_asyncio.exit
	def loop_asyncio_exit(kernel):

How it happened:
The @register_integration("asyncio") and def loop_asyncio(kernel): was at the old ages, to drive the asyncio codes that inputed by users, like asyncio.ensure_future(...), when ipykernel was running under IOloop of tornado<6.1 which using the selectorloop or even older type eventloop. It was to make users able to run asyncio codes when the underhood is other things.
The current ipykernel its main loop is already asyncio loop, by IOloop of tornado>6.1. The user inputed asyncio codes already run in the main loop.

Therefore the related codes @register_integration("asyncio") and def loop_asyncio(kernel): could be deleted.

Solution:
related issue: #1469 solving the proactor and selector eventloop within asyncio