* crypto: ensure that VerifySignature rejects malleable signatures
It already rejected them when using libsecp256k1, make sure the nocgo
version does the same thing.
* crypto: simplify check
* crypto: fix build
We need those operations for p2p/enr.
Also upgrade github.com/btcsuite/btcd/btcec to the latest version
and improve BenchmarkSha3. The benchmark printed extra output
that confused tools like benchstat and ignored N.
