Update AP Transformers, remove legacy OStatus methods

app/Transformer/ActivityPub/ProfileOutbox.php

@@ -50,7 +50,6 @@ class ProfileOutbox extends Fractal\TransformerAbstract
             'sensitive' => (bool) $i->is_nsfw,
             'atomUri' => $i->url(),
             'inReplyToAtomUri' => null,
-            'conversation' => $i->url(),
             'attachment' => [
 
               // TODO: support more than 1 attachment

app/Transformer/ActivityPub/StatusTransformer.php

@@ -46,7 +46,6 @@ class StatusTransformer extends Fractal\TransformerAbstract
           'sensitive' => (bool) $status->is_nsfw,
           'atomUri' => $status->url(),
           'inReplyToAtomUri' => null,
-          'conversation' => $status->url(),
           'attachment' => $status->media->map(function($media) {
             return [
               'type' => 'Document',