Remove app metadata from scrobble payloads

The Trakt scrobble API only requires progress and the media object.
Sending undocumented app_version/app_date fields with null values
causes 400 responses from the API.

Fixes #100

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: glensc

trakt/sync.py

@@ -607,8 +607,7 @@ def _post(self, uri):
 
         :param uri: The uri to post to
         """
-        payload = dict(progress=self.progress, app_version=self.version,
-                       date=self.date)
+        payload = dict(progress=self.progress)
         payload.update(self.media.to_json_singular())
         response = yield uri, payload
         yield response