Homepage updater: specify table alias for anonymous_receiving

Fixes #2247 by specifying the table name.

It seems the only people who could review this are @zwn and @whit537.

Let me know if I misunderstood the purpose of the conditions on the subquery for `homepage_top_receivers`. (I switched around whether the tipper or the tippee was being checked)

Note that for `homepage_top_givers` `p` is the tipper and `p2` is the tippee while for `homepage_top_receivers` those are reversed. I did this to make `p` the main subject in both queries.