Hotfix: Update jcb to avoid git-lfs files (#2782)

Removes git-lfs files from the `GDASApp` `jcb` submodule, allowing it to
be cloned on Hera.

This hotfix points to a non-authoritative branch of the GDASApp
(https://github.com/DavidHuber-NOAA/GDASApp/tree/hotfix/update_jcb) and
should be updated ASAP back to the authoritative repository.