Remove dependency checkers from uSync core.

[KevinJump]

With v8.7 we have made dependency checkers load by type, so we no longer need them declared inline for the handlers to work.

this means we can move them out of the core project into uSync.Complete where they are used. this streamlines the testing/development of the checkers as they are now in the correct project. It also reduces the requirement on any third party handler/serializer as you no longer 'need' to develop a dependency checker as part of the process (unless you want it to also work with uSync.Complete.