May as well add it to the .reg file you cart around on your thumb drive. I have one that already disables all the Windows "consumer features" and turns off all the lock screen nags, Cortana (this is no longer relevant, though), etc.

It's in:

HKCU\Software\Policies\Microsoft\Windows\WindowsCopilot

And also:

HKLM\Software\Policies\Microsoft\Windows\WindowsCopilot

In both locations, create a DWORD "TurnOffWindowsCopilot" and set it to 1. Reboot.