feat: allow hardlinks in the system extension images

They should cause no harm as every extension as an image on its own, so
hardlinks are only available between the files in one image only.

Signed-off-by: Andrey Smirnov <andrey.smirnov@talos-systems.com>

internal/pkg/extensions/validate.go

@@ -10,7 +10,6 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"syscall"
 
 	hashiversion "github.com/hashicorp/go-version"
 
@@ -70,18 +69,6 @@ func (ext *Extension) validateContents() error {
 			return fmt.Errorf("world-writeable files are not allowed: %q", itemPath)
 		}
 
-		var st fs.FileInfo
-
-		st, err = d.Info()
-		if err != nil {
-			return err
-		}
-
-		// no hardlinks
-		if !d.IsDir() && st.Sys().(*syscall.Stat_t).Nlink > 1 {
-			return fmt.Errorf("hardlinks are not allowed: %q", itemPath)
-		}
-
 		// no special files
 		if !d.IsDir() && !d.Type().IsRegular() && d.Type().Type() != os.ModeSymlink {
 			return fmt.Errorf("special files are not allowed: %q", itemPath)