fix: remove unused parameters from grub cmdline

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

builder.go

@@ -165,6 +165,11 @@ func NewBuilder(ctx context.Context, workdir, imgTag, disk string, size uint64,
 		return nil, err
 	}
 
+	if !bl.Static() {
+		config.Kernel = ""
+		config.Initrd = ""
+	}
+
 	if size == 0 {
 		size = 10 * uint64(datasize.GB)
 	}