Rewrite asyncio.wait_for using asyncio.timeout

Over the years a lot of issues have accumulated for asyncio.wait_for and the code has become complicated. The asyncio.timeout can be used to simplify this a lot and will also fix bugs which are already fixed or don't exist in asyncio.timeout. This rewrite won't be backported. asyncio.wait_for should be nothing more than a wrapper around asyncio.timeout.