Removing a VPC configuration doesn't reset to defaults of "No VPC"

0.7.3-pro

## Description

When removing a vpc configuration, a following deployment doesn't reset the deployment to the default "No VPC"

## Steps to Reproduce

Remove a VPC configuration from `up.json` and re-deploy.
https://media.dev.unee-t.com/2018-09-05/up-sg.mp4

Work around is to `up stack delete` and re-deploy, which obviously takes a lot longer.