node/p2p: consider deprecating TCP usage

[Wondertan]

After #913 is merged. we will have both TCP and QUIC support, and we should consider dropping TCP support entirely.

[liamsi]

I'd recommend not prioritizing this. It might be good to make this a post-launch concern even.

[Wondertan]

No objections.

Also note that this can be done in two simple stages:

• Removing 2 loc from default config to prevent nodes listening on TCP by default
  • New nodes won't run it
  • Still able to connect to TCP nodes
  • Suggest removing TCP from configs to existing nodes
• Removing transport support entirely from libp2p constructor
  • Once we know there is no TCP nodes running(e.g. via Crawler)