internal/rosa: remove calls to low-level exec helper

This method predates the helper infrastructure, it is awkward to use and difficult to maintain for the replacement bootstrap mechanism. This change prepares for its removal.

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

internal/rosa/rosa.go

@@ -363,9 +363,14 @@ function apply {
 			buf.WriteString("'\n")
 		}
 	}
-	return t.New(name+"-src", 0, t.Append(nil,
+
+	return t.NewPackage(name+"-src", Unversioned, nil, &PackageAttr{
+		Paths: paths,
+	}, &GenericHelper{
+		Build: buf.String(),
+	},
 		_patch,
-	), nil, nil, buf.String(), paths...)
+	)
 }
 
 // helperInPlace is a special directory value for omitting the cd statement.