remove needless imports

mobile/lib/shared/models/asset.dart

@@ -1,6 +1,4 @@
 import 'dart:convert';
-import 'dart:ffi';
-import 'dart:typed_data';
 
 import 'package:immich_mobile/shared/models/exif_info.dart';
 import 'package:immich_mobile/shared/models/store.dart';