bpo-42392: Remove loop parameter from asyncio.streams

[uriyyo]

Remove loop parameter from asyncio.open_connection and asyncio.start_server functions.

This PR is a part of the loop parameter removal that should be done in the scope of python 3.10.

https://bugs.python.org/issue42392

[uriyyo]

@1st1 @asvetlov

I have a question regarding classes defined in asyncio.streams.
Those classes accept loop parameters, maybe it makes sense to rewrite them to use the new _LoopBoundMixin class?

[asvetlov]

Sure yes. Good idea.

[asvetlov]

Thanks!

[uriyyo]

@asvetlov I ended up with not using _LoopBoundMixin for classes defined in asyncio.streams because there was no deprecation warning regarding loop parameter removal so I think it can lead to some unpredictable bugs in user code.

[asvetlov]

Both fine with me. These constructors are private, people should not use them directly. But some code can violate this principle.