js_image_layer.bzl should not depend on rules_python directly.

[thesayyn]

Currently, js_image_layer is using rules_python to create a proxy py_binary that passed down to pkg_tar#build_tar to fix up manifest for symlinks. We should migrate that to js_binary instead.

[alexeagle]

Rather than port this program to nodejs, I think we'll just wait for rules_pkg to support symlinks. We'll continue to have that transitive dependency on rules_python, sadly.