Removing older version of Prepar3D from Orbx Central

Orbx Central requires both a registry entry, 

HKEY_CURRENT_USER\SOFTWARE\Lockheed Martin\Prepar3D v4\AppPath\the path to where you installed P3D v4 that points to your installation and a folder there which contains Prepar3D.exe.

If both those are present, Orbx Central will show P3D v4 as installed on the machine. Uninstalling and deregistering P3D v4 removes the registry entries.