Dont compute p_astro for spiir allsky

The spiir team has reached out and said they're ready to start uploading their own p_astro, so this MR stops computing p_astro for them. I'm waiting on them for confirmation that this is only for the allsky search (not the earlywarning search), and a final sign off that they're ready for us to turn this off. After approval I'll wait to merge until they confirm they're ready.

Edit 23-04-19: The spiir team is okay with us doing this now.