internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/util-linux.go

@@ -11,11 +11,11 @@ func (t Toolchain) newUtilLinux() (pkg.Artifact, string) {
 		version  = "2.42"
 		checksum = "Uy8Nxg9DsW5YwDoeaZeZTyQJ2YmnaaL_fSsQXsLUiFFUd7wnZeD_3SEaVO7ClJlk"
 	)
-	return t.NewPackage("util-linux", version, pkg.NewHTTPGetTar(
-		nil, "https://www.kernel.org/pub/linux/utils/util-linux/"+
+	return t.NewPackage("util-linux", version, newTar(
+		"https://www.kernel.org/pub/linux/utils/util-linux/"+
 			"v"+strings.Join(strings.SplitN(version, ".", 3)[:2], ".")+
 			"/util-linux-"+version+".tar.gz",
-		mustDecode(checksum),
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		ScriptEarly: `