Generated by go1.17 fmt ./...

Original change by @jpeletier 

Package crypto works with or without cgo, which is great. However, to make it
work without cgo required setting the build tag `nocgo`. It's common to disable
cgo by instead just setting the environment variable `CGO_ENABLED=0`. Setting
this environment variable does _not_ implicitly set the build tag `nocgo`. So
projects that try to build the crypto package with `CGO_ENABLED=0` will fail. I
have done this myself several times. Until today, I had just assumed that this
meant that this package requires cgo.

But a small build tag change will make this case work. Instead of using `nocgo`
and `!nocgo`, we can use `!cgo` and `cgo`, respectively. The `cgo` build tag is
automatically set if cgo is enabled, and unset if it is disabled.

This adds the inverse to DecompressPubkey and improves a few minor
details in crypto/secp256k1.

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.

* common/math: optimize PaddedBigBytes, use it more

name              old time/op    new time/op    delta
PaddedBigBytes-8    71.1ns ± 5%    46.1ns ± 1%  -35.15%  (p=0.000 n=20+19)

name              old alloc/op   new alloc/op   delta
PaddedBigBytes-8     48.0B ± 0%     32.0B ± 0%  -33.33%  (p=0.000 n=20+20)

* all: unify big.Int zero checks

Various checks were in use. This commit replaces them all with Int.Sign,
which is cheaper and less code.

eg templates:

    func before(x *big.Int) bool { return x.BitLen() == 0 }
    func after(x *big.Int) bool  { return x.Sign() == 0 }

    func before(x *big.Int) bool { return x.BitLen() > 0 }
    func after(x *big.Int) bool  { return x.Sign() != 0 }

    func before(x *big.Int) int { return x.Cmp(common.Big0) }
    func after(x *big.Int) int  { return x.Sign() }

* common/math, crypto/secp256k1: make ReadBits public in package math

* vendor: add github.com/btcsuite/btcd/btcec

* crypto: add btcec fallback for sign/recover without cgo

This commit adds a non-cgo fallback implementation of secp256k1
operations.

* crypto, core/vm: remove wrappers for sha256, ripemd160