update the localdev grid's secrets and other configuration to reflect this

testing and production are broken by this commit since they have not been
updated similarly

It is no longer required to add IP addresses to the Vagrant-generated ssh
configuration because the Vagrant-configured hostnames now match up with the
names morph will try to use to connect to the VMs.

Just require hostName and domain instead of an extra publicIPv4 option.  Leave
behind a similar option, `publicAddress`, just in case it needs to be
overridden at some point, but stop supplying a value for it anywhere.

Put its contents in it and then use them from there instead of importing them
all over the rest of the code.

Remove the VirtualBox GUI, see
https://search.nixos.org/options?channel=21.05&show=virtualisation.virtualbox.host.headless&from=0&size=50&sort=relevance&query=virtualbox

... if you are reading this not in the repo, but from the web page, you might
not know where to go to make all those nice commands work.

... clean up 

Less (SLOC) is more