Use crypto/sha256 (#29386)

Go 1.21 improved the performance of `crypto/sha256`. It's now similar to
`minio/sha256-simd`, so we should just use the standard libs.

https://go.dev/doc/go1.21#crypto/sha256
https://go-review.googlesource.com/c/go/+/408795
https://github.com/multiformats/go-multihash/pull/173

modules/util/keypair_test.go

@@ -7,12 +7,12 @@ import (
 	"crypto"
 	"crypto/rand"
 	"crypto/rsa"
+	"crypto/sha256"
 	"crypto/x509"
 	"encoding/pem"
 	"regexp"
 	"testing"
 
-	"github.com/minio/sha256-simd"
 	"github.com/stretchr/testify/assert"
 )