Add a way to uninstall the wintun driver from the system

~~The installer should come with `wintun.dll` to be dropped in the same directory we will be downloading the VPN binary to. It should also install the driver during installation, and uninstall it during uninstallation. This could either be by delegating the install/uninstall to the Go code, or importing the DLL in the installer and calling the correct method.~~

~~We will most likely need to check-in `wintun.dll` to this repo.~~

We ship `wintun.dll` and it gets automatically loaded by the Go code, but we should add some method of uninstalling the system driver from the system on user request. Tailscale does this by having a signal you can send to the system service to have it uninstall the driver.

Start by reading the Go code that automatically loads wintun.dll and the system service entry point responsible for driver handling. Compare the requested user-triggered uninstall behavior with Tailscale's signal-based approach; done means a user request can signal the service and remove the system driver safely.

Written by the indexing model from the issue text.