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/llvm_test.go

@@ -8,7 +8,7 @@ import (
 )
 
 func TestLLVMInputs(t *testing.T) {
-	const wantInputCount = 688
+	const wantInputCount = 857
 
 	_, llvm := rosa.Native().Std().MustLoad(rosa.H("llvm"))
 	var n int