Drop trailing blank line in player.rs

Removing the `MpvExt` trait left an empty trailing line that `cargo fmt
--check` rejects in CI.

https://claude.ai/code/session_01CuGHFREBZFkf8tfaiRV4K6

src/stremio_app/stremio_player/player.rs

@@ -269,4 +269,3 @@ fn create_message_thread(
         }
     })
 }
-