Change Alerce dataset to use a new collection

I've just converted the alerce catalog to a collection with nested columns and put it in the same Epyc directory as the currently exposed `alerce-nested` is. Let's point data.lsdb.io to that new collection and remove the `alerce-nested` catalog.

That would be a breaking change, and we will also need to change this documentation notebook to support it (actually simplify it by removing nesting code)
https://docs.lsdb.io/en/latest/tutorials/pre_executed/ztf-alerts-sne.html