"do you still have the .msi? Perhaps you can run it with msiexec /u? Or re-install it again?
Basically, it should be impossible that a .msi does not create an uninstall entry (and will not be rolled back when you try to install any other .msi). If you removed the uninstall entry manually, you can still uninstall it via msiexec /u, but you will need to find the installer GUID for that (which can be hard to find if you have a lot of stuff installed...)
If that fails: The entries themselves are in the registry at HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Keyboard Layouts, so you can at least remove the entry for your layout (if not uninstall the .dll and stuff)."