Remove outdated todo list from the repository

• We have following data models in the libaccounts-qt
  • AccountsModel
  • ProvidersModel
  • AccountsServiceModel
• We don't need KDE signon-ui as there exists already Qt based signon-ui
• There exists already qt based singond oauth2 and password plugins
• ktp code is no-longer part of kaccounts-integration
• akonadi code is in work-in-progress
• kio-webdav already is running as kaccount plugin
• There already exists signon-kwallet-extension