This updates the no-cgo implementations in the crypto package to use
the github.com/btcsuite/btcd/btcec/v2 module instead of the older btcec
package that was part of the main github.com/btcsuite/btcd module.
name old time/op new time/op delta
EcrecoverSignature-32 198µs ± 0% 144µs ± 0% -27.11%
VerifySignature-32 177µs ± 0% 128µs ± 0% -27.44%
DecompressPubkey-32 20.9µs ± 0% 10.1µs ± 0% -51.51%
Use (*ModNScalar).IsOverHalfOrder instead of math/big.Int when checking
for malleable signatures.
830231c1c4