[ActivityPub] Fix some small known problems

ActivityPubPlugin:
- Rework onProfileDeleteRelated to account for the tables _rsa and _pending_follow_requests
- Update onEndShowAccountProfileBlock to stop creating the ap_profile if it doesn't exist (we'll handle this in a different manner)

Activitypub_profile:
- Remove unnecessary code from from_profile method and add return type information

Explorer:
- Update travel_collection to call itself instead of _lookup, that was wrong

plugins/ActivityPub/lib/explorer.php

@@ -450,7 +450,7 @@ class Activitypub_explorer
         }
         // Go through entire collection
         if (!is_null($res["next"])) {
-            $this->_lookup($res["next"]);
+            $this->travel_collection($res["next"]);
         }
 
         return true;