remove n^2 part of person triggers, improve community aggregate trigger

[phiresky]

This PR has two changes:

1. it removes the O(n^2) part of the person_aggregates_comment_count and person_aggregates_post_count triggers. This part has never actually worked due to the use of coalesce(0, ...). See SQL Trigger/function 'person_aggregates_comment_count' is broken #2910 . In order to fix the function and not make it be too expensive, the triggers would have to get an enforced order or be merged into one trigger (some effort in post UPDATE trigger focused on all the combined actions of a byebye a… #3727, but incomplete so far)
2. it removes an unnecessary select in the community trigger that loops through all comments on a post on post delete (see https://gist.github.com/phiresky/402999658552f70af2ade151bc8ded34 for a comparison in query plans)

This is part of the solution to #3528. After this and #3732, the only expensive trigger remaining should be community_aggregates_post_count.

[phiresky]

I've commented out the person_aggregates comment_score test part, because that only ever accidentally succeeded - the comment delete in that test deletes the only comment, so a resulting score of 0 is correct. But in reality, a delete always sets the score to 0 even if it shouldn't be.