Remove WOSingleton dependency from WORegistrationController (WOCommon, 515521f)

Although there should never be any need to have more than one instance of WORegistrationController active at any time, there is no real need to enforce singleton behaviour either. A single WORegistrationController instance is generally instantiated in a nib rather than programmatically so there should never be more than one instance at a time anyway; even if there were it would be completely harmless.

So this commit removes the dependency on WOSingleton as it is an unnecessary complication.

Signed-off-by: Greg Hurrell <greg@hurrell.net>