Don't look through gracedb logs for p-astro and embright data products if we don't expect an event to have them

Right now the preliminary_initial_update_alert function downloads gracedb logs from a superevent to retrieve the filenames of the skymap, embright, and p-astro files if we don't have the filename when the function is called. This results in times where we have a superevent that we don't expect to have a p-astro or embright file for causing us to query gracedb for the logs to find files that won't exist.