When you install your Web App Gallery through Web Platform Installer, you might ask how to delete the application.
As Windows do not provide MSI or installer, hence you are not able to easily remove them from Window Programs Menu.
However, when you using IIS7.x and above you do come with Web Deployment Tool(Web Deploy).
There are two options depending on which node you have install to the IIS.
Web Site Deploy: Delete Web Site and Content
Application Deploy: Delete application and Content