update overall module structure, remove host-specific config files

- update flake.nix to reflect new structure
- update modules/default.nix imports
- update modules/network.nix and wireguard.nix
- remove config/configuration.nix and hardware-configuration.nix
- remove modules/access.nix from this module's scope

modules/default.nix

@@ -1 +1 @@
-{ config, pkgs, ... }: { imports = [ ./access.nix ./network.nix ]; }
+{ config, pkgs, ... }: { imports = [ ./network.nix ./wireguard.nix ]; }