discover_chromecasts is available on current releases despite marked as removed in code

[discover_chromecasts](https://github.com/home-assistant-libs/pychromecast/blob/c5bbf513e80d6772dbf0ab50c12a62f38c43eaa7/pychromecast/discovery.py#L709-L711)

Would be nice to either actually remove it now (and close issues related to it) or bump the date up