Revert of Avoid disconnect UI from writing 'undefined' to the VPN host (patchset...

Revert of Avoid disconnect UI from writing 'undefined' to the VPN host (patchset #1 id:20001 of https://codereview.chromium.org/769873002/)

Reason for revert:
This is not the right fix to the problem.

Original issue's description:
> Avoid disconnect UI from writing 'undefined' to the VPN host
>
> When disconnecting from a VPN configuration created by an
> extension, the disconnect UI sets the host property of the
> VPN configuration to 'undefined'. This makes the
> configuration unusable after a reboot. This CL eliminates the
> write when it is 'undefined'.
>
> BUG=407541
>
> Committed: https://crrev.com/1eb3c92e8bd73686cf68dd0a8e701750cd2322fd
> Cr-Commit-Position: refs/heads/master@{#306193}

TBR=pneubeck@chromium.org,stevenjb@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=407541

Review URL: https://codereview.chromium.org/774613004

Cr-Commit-Position: refs/heads/master@{#306371}