Reference nix-dram package directly from inputs

This should avoid patches not working because our pkgs
follows nixos = release-21.11 and nix-dram follows nixos-unstable

flake.nix

@@ -81,7 +81,6 @@
               nur.overlay
               agenix.overlay
               nvfetcher.overlay
-              nix-dram.overlay
               ./pkgs/default.nix
             ];
           };

profiles/core/default.nix

@@ -85,7 +85,8 @@ in
     };
 
     nix = {
-      package = pkgs.nix-dram;
+      # use nix-dram, a patched nix command, see: https://github.com/dramforever/nix-dram
+      package = inputs.nix-dram.packages.${pkgs.system}.nix-dram;
 
       # Improve nix store disk usage
       autoOptimiseStore = true;