Remove btcsuite/btcd dep

[MarcoPolo]

I don't think need to pull in this btcd dependency. btcec is now it's own module.

This will also prevent us from forcing the btcd dep upgrade on downstream users. It breaks somethings especially https://github.com/whyrusleeping/ledger-filecoin-go which is used by lotus.

[marten-seemann]

Will we run into the problem fixed in #254 again?

My conclusion back then was that this will have to wait until we stop using Go 1.17.

[MarcoPolo]

go checks pass, so maybe not?

I think removing this dep would side step that problem by not having btcd to conflict with.

[MarcoPolo]

Was able to sucessfully remove this dep from go-libp2p as well which unblocked lotus from being able to update: filecoin-project/lotus#8970

[marten-seemann]

go checks pass, so maybe not?

The checks passed in this repo, but not when updating go-libp2p to the new version. I'm ok with merging this (actually, I'd be very happy to get rid of this hack!!), but we should make sure that go-libp2p will still pass CI when we make this change.
More details in #252.

[MarcoPolo]

The checks passed in this repo, but not when updating go-libp2p to the new version.

Seems like the tests are passing in go-libp2p too: libp2p/go-libp2p#1641

[marten-seemann]

Then let’s get rid of this hack!