Update submodule to contain public flux repo

[jlazar17]

I want to update the submodules to link against the public SN flux directory rather than the private one. It seems strange that the project is effectively not open source because the SN fluxes are hidden in a private repo

[sgriswol]

Reviving this after a very long period of neglect for this issue.

The public flux repository and the private flux repository (snfluxes) are both defunct as of SNEWPY's integration with ASTERIA. SNEWPY now provides access to a much broader library of SN models than those maintained in these repositories. Additionally, SNEWPY is maintained by a dedicated team on SNEWS 2.0.

I'm classifying this as wontfix, because I don't think we are interested in re-integrating these model repositories, but I am not closing the issue now because additional discussion about documentation or cleanup may be warranted.