Remove btcsuite/btcd dep (#272)

core/crypto/btcd_go116.go

@@ -1,13 +0,0 @@
-//go:build !go1.17
-// +build !go1.17
-
-package crypto
-
-// This import allows us to force a minimum version of github.com/btcsuite/btcd,
-// which otherwise causes problems when `go mod tidy` tries to please Go 1.16
-// (which we don't care about any more at this point).
-//
-// See https://github.com/libp2p/go-libp2p-core/issues/252 for details.
-import (
-	_ "github.com/btcsuite/btcd/chaincfg"
-)