Tomtom not updating to the new re-imaged version is a known issue on their forums, the fix is to just delete the old version as they use a completely new payment subscription system now.
My older license which I had for Go Navigation are maximum 3 year subscriptions and were able to be upgraded to the new Go Mobile which kept your license for the remainder of it's term and from then on the new subscription system is in place.
Sounds like your license is even older so it's definitely redundant, you'll probably find that once you delete the app it wont be available again in the store, being the new version has so many changes it's generally better to install clean rather than upgrade anyway.