There is nothing to uninstall. If you wish to stop using the AppDog web app for iOS, all you need to do is stop visiting https://m.appdog.com/.
A lot of users (reasonably) think they installed something during AppDog registration. However, no software is actually installed. You can read about what happens during registration here.
If you really want all traces of AppDog off of your device you can clear the cookies that we store in Safari. Be aware, however, that when you do this, you are erasing cookies from all web sites.