perf: closes #13145, reduce calls in actors.prune

instead of deleting 18k users everyday delete max 500 every 30mins like notifications.prune

refactor getLocalFollowCounts so it works with an array of actors

dont make dbcalls for uids that dont exist

src/activitypub/index.js

@@ -68,7 +68,7 @@ ActivityPub.startJobs = () => {
 		}
 	}, null, true, null, null, false); // change last argument to true for debugging
 
-	new CronJob('0 1 * * *', async () => {
+	new CronJob('*/30 * * * *', async () => {
 		try {
 			await ActivityPub.actors.prune();
 		} catch (err) {