How do I get rid of orphaned application entries after uninstallation?
The MobileCal.app is part of Xcode's iPhone SDK, so the easiest way to get rid of that app is to either remove the Xcode completely or remove just the app. The file can be located inside the Xcode package:

Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/Applications