refactor(x1): remove unused IPU6 module

- Deleted `ipu.nix` and its reference in `default.nix` under `x1` systems.
- Simplifies configuration by removing unused and commented-out code.

systems/x86_64-linux/x1/default.nix

@@ -9,7 +9,6 @@ with lib.metacfg;
 {
   imports = [
     ./hardware-configuration.nix
-    ./ipu.nix
   ];
 
   services.cratedocs-mcp.enable = true;