Completely uninstall the subsystem for Linux on Win10?

If your OS has been upgraded to the Fall Creators Update, you should be able to issue the command wslconfig.

You could of course try uninstalling first by using the command lxrun /uninstall /full.

If its still there, you can try unregistering the distro:

• First you need to know which distro is installed by using

  wslconfig /l
  

• From the list choose the distro (e.g. Ubuntu) you want to uninstall and type the command

  wslconfig /u Ubuntu
  

In order to disable WSL, one has to go back into

Control Panel -> programs-features -> turn on/off Windows features and deselect Windows Subsystem for Linux, and Save.