[Typing-sig] Re: Removing `async` keyword form PEP 677

I'm fine with removing `async` from the spec. I think it's a reasonable simplification and eliminates some of the special-case parsing, as mentioned in the python-dev thread. That same thread also mentions the `**` syntax for ParamSpecs. I'm OK eliminating this too. As someone mentioned, it requires special-case parsing, is not needed for correct semantic analysis, and (IMO) adds relatively little in the way of readability. I'm also OK leaving it in if others feel strongly about it and it doesn't become an obstacle for PEP 677 ratification. -Eric