BUG DOC: module docs in solarsystem is broken for some modules

[bsipocz]

solarsystem is just an alias namespace for a couple of modules, e.g imcee, but unfortunately navigating to the module from the solarsystem module is broken, and instead we rendered there an empty docs page.

E.g. https://astroquery.readthedocs.io/en/latest/solarsystem/imcce/imcce.html which should instead point back to https://astroquery.readthedocs.io/en/latest/imcce/imcce.html