feat(wpcarro/diogenes): Nixify diogenes's Terraform configuration

TL;DR:
- Define googleCloudVM function to provision NixOS VMs on Google Cloud.
- Consume googleCloudVM in diogenes/default.nix
- Define README.md for basic usage instructions (subject to change).
- Delete diogenes's HCL
- Remove `diogenesSystem` from meta.targets

I'm still having trouble with DNS:
- I need to transfer the Google Domains config to Cloud DNS
- `host billandhiscomputer.com` is NXDOMAIN, so I don't trust my tf DNS config
- This is preventing me from getting SSL certs, which blocks my website, quassel

Change-Id: If315876c96298e83a5953f13b62784d2f65a1024
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4747
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/nixos/default.nix

@@ -1,9 +1,8 @@
-{ depot, lib, ... }:
+{ depot, ... }:
 
 let systemFor = sys: (depot.ops.nixos.nixosFor sys).system;
 in {
-  diogenesSystem = systemFor depot.users.wpcarro.nixos.diogenes;
   marcusSystem = systemFor depot.users.wpcarro.nixos.marcus;
 
-  meta.targets = [ "diogenesSystem" "marcusSystem" ];
+  meta.targets = [ "marcusSystem" ];
 }