modules: refactor module bootstrapping

Let's simplify things by defining all modules in `./plugins`, `./modules`
and `./wrappers/modules`.

Instead of currying `pkgs` into a bootstrapping module, we can require
`defaultPkgs` be provided as a special arg.

This refactor allows us to completely remove `flake-modules/modules.nix`!

modules/misc/default.nix

@@ -0,0 +1,13 @@
+{ defaultPkgs, ... }:
+let
+  # We can't use config._module.args to define imports,
+  # so we're forced to use specialArgs.defaultPkgs's path
+  nixosModules = defaultPkgs.path + "/nixos/modules/";
+in
+{
+  imports = [
+    ./nixpkgs.nix
+    ./nixvim-info.nix
+    (nixosModules + "/misc/meta.nix")
+  ];
+}