Restructure flake.nix for a simpler config for building different images off the same NixOS config.

nix/configuration/roles/wasm/default.nix

@@ -2,7 +2,6 @@
   config,
   lib,
   pkgs,
-  pkgs-unoptimized,
   ...
 }:
 
@@ -18,23 +17,11 @@
     };
   };
 
-  config = lib.mkIf config.me.wasm.enable (
-    lib.mkMerge [
-      {
-        environment.systemPackages = with pkgs; [
-          wabt
-          wasm-bindgen-cli
-          binaryen # for wasm-opt
-        ];
-
-        nixpkgs.overlays = [
-          (final: prev: {
-            inherit (pkgs-unoptimized)
-              binaryen
-              ;
-          })
-        ];
-      }
-    ]
-  );
+  config = lib.mkIf config.me.wasm.enable {
+    environment.systemPackages = with pkgs; [
+      wabt
+      wasm-bindgen-cli
+      binaryen # for wasm-opt
+    ];
+  };
 }