Remove Stream methods from `Connection` interface

[maschad]

Following up from the discussion here the muxers should be ultimately responsible for managing streams as opposed to the connections themselves

[tabcat]

I'm going to look a bit closer but seems like this requires moving the functionality of what is currently (add|remove)Stream and putting that on the muxer interface?

[maschad]

There wouldn't be any use for adding those methods to the stream muxer interface since we already have the newStream and close methods so these methods just need to be removed from the connection interface.

@mmsaki actually began work on this on #1829 but I am not sure what the status of that is now. Perhaps they can provide an update.