Move mpi to index

pkgs/index.nix

@@ -22,6 +22,7 @@ let
     intelPackages_2023 = callPackage ./intel-oneapi/2023.nix { };
     jemallocNanos6 = callPackage ./nanos6/jemalloc.nix { };
     #lmbench = callPackage ./lmbench/default.nix { }; # Broken
+    mpi = final.mpich; # Set MPICH as default
     mcxx = callPackage ./mcxx/default.nix { };
     nanos6 = callPackage ./nanos6/default.nix { };
     nanos6Debug = final.nanos6.override { enableDebug = true; };

pkgs/overlay.nix

@@ -1,8 +1,5 @@
 final: prev:
 {
-  # Set MPICH as default
-  mpi = final.mpich;
-
   # Configure the network for MPICH
   mpich = with final; let
     # pmix comes with the libraries in .out and headers in .dev