feat: remove broken spdy multiplexer and enable multiplex by default as second option

[dignifiedquire]

• spdystream is not fully spdy spec compatible, creating issues when
  doing interop with js, so it is removed
• muliplex is working well now in interop with js, so being enabled by
  default

This means the new default muxers are yamux,mplex

[whyrusleeping]

@dignifiedquire fix your commit signature

[whyrusleeping]

Lets leave the command line flag in, so that users can disable it if they want (im still considering it experimental). Lets also do something like:

if os.Getenv("IPFS_ENABLE_SPDY") == "true" {
  // add spdy muxer
}

So that it becomes easier to test this if we get around to fixing the go spdy implementation. (which i think is something we want to do eventually? or maybe replace it with http2, idk, probably can keep the spdy stuff removed)

Yeah, disregard the bit about spdy.

[dignifiedquire]

what's wromg with it? I already pushed a fix with the license stuff

[dignifiedquire]

@whyrusleeping I think I did what you want

[whyrusleeping]

LGTM, thanks @dignifiedquire

[Kubuxu]

This should have, but did not remove spdy from package.json. I will handle it.