refactor: use new mail interface desing

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Providers/CollectionResource.php

@@ -91,12 +91,4 @@ class CollectionResource extends CollectionMutableAbstract
         return $this->properties;
     }
 
-    // ── JSON ─────────────────────────────────────────────────────────────────
-
-    public function jsonSerialize(): array
-    {
-        $data                      = $this->data;
-        $data['properties']        = $this->getProperties()->jsonSerialize();
-        return $data;
-    }
 }