Command line to remove an environment variable from the OS level configuration

Question

Windows has the setx command:

Description:
    Creates or modifies environment variables in the user or system
    environment.

So you can

Answer 1

The command in DougWare's answer did not work, but this did:

reg delete "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment" /v FOOBAR /f

The shortcut HKLM can be used for HKEY_LOCAL_MACHINE.