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

tests/integration/api_packages_chef_test.go

@@ -11,6 +11,7 @@ import (
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/sha1"
+	"crypto/sha256"
 	"crypto/x509"
 	"encoding/base64"
 	"encoding/pem"
@@ -33,7 +34,6 @@ import (
 	chef_router "code.gitea.io/gitea/routers/api/packages/chef"
 	"code.gitea.io/gitea/tests"
 
-	"github.com/minio/sha256-simd"
 	"github.com/stretchr/testify/assert"
 )