internal/pkg: remove tar built-in decompressor

This is replaced by decompressArtifact and is no longer necessary.

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

internal/rosa/go.go

@@ -16,7 +16,7 @@ func (t Toolchain) newGo(
 	return t.NewPackage("go", version, newTar(
 		"https://go.dev/dl/go"+version+".src.tar.gz",
 		checksum,
-		pkg.TarGzip,
+		pkg.Gzip,
 	), &PackageAttr{
 		EnterSource: true,
 		Env: slices.Concat([]string{
@@ -79,7 +79,7 @@ func init() {
 			bootstrapEarly = []pkg.Artifact{t.NewPackage("go", "1.4-bootstrap", newTar(
 				"https://dl.google.com/go/go1.4-bootstrap-20171003.tar.gz",
 				"8o9JL_ToiQKadCTb04nvBDkp8O1xiWOolAxVEqaTGodieNe4lOFEjlOxN3bwwe23",
-				pkg.TarGzip,
+				pkg.Gzip,
 			), &PackageAttr{
 				EnterSource: true,
 				Env: []string{