Remove vestigial `NodeTo*Version` constructors

[nfrisby]

Now that mainnet is in the Mary era, we need not successfully connect to peers that can't participate in the Mary era. Thus we can simplify the code by removing those older negotiable versions and whatever backwards-compatibility logic they've been carrying along in eg our serializers.

cc @coot

[dnadales]

Should we duplicate this issue in ouroboros-consensus?

[nfrisby]

I don't think we need to duplicate this issue, since the integration of whichever ouroboros-network version includes this change will force the dead code to be reaped etc.

[nfrisby]

@coot I removed the consensus labels---despite me opening it, this is a proper networking Issue, I think.

[amesgen]

Old NodeToNode versions were removed in #4985

What about also removing old NodeToClient versions?

[coot]

@amesgen do you have an advise which versions should be removed?

[amesgen]

Node 9.0.0/9.1.0 use latestReleasedNodeVersion = NodeToClientV_16 (src), and as every node must have upgraded to at least this version since Conway, we could remove everything below NodeToClientV_16.