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/lfs/pointer.go

@@ -4,6 +4,7 @@
 package lfs
 
 import (
+	"crypto/sha256"
 	"encoding/hex"
 	"errors"
 	"fmt"
@@ -12,8 +13,6 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
-
-	"github.com/minio/sha256-simd"
 )
 
 const (