Fix processing of incoming Block activities (#15546)
Fix processing of incoming Block activities (#15546)

Unlike locally-issued blocks, they weren't clearing follow
relationships in both directions, follow requests or notifications.

Co-authored-by: Claire <82b964c50e9d1d222e48cf5046e6484a966a7b07@sitedethib.com>
koba-lab/mastodon,koba-lab/mastodon,koba-lab/mastodon,koba-lab/mastodon