Delete unused templates skeleton and app_shared and release as 5.0.0. (#8360)

Towards flutter/flutter#160692.

The last thing I'll do is update the dependency in `flutter_tools` to `flutter_template_images: 5.0.0`.

Author: matanlurey

packages/flutter_template_images/CHANGELOG.md

@@ -2,7 +2,7 @@ name: flutter_template_images
 description: Image files for use in flutter_tools templates without adding binary files to flutter/flutter.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_template_images
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_template_images%22
-version: 4.3.0
+version: 5.0.0
 
 environment:
   sdk: ^3.4.0