Revert "fix #150: enable min-free and max-free GC"

This reverts commit e4ae363.

for-upstream/gc.nix

@@ -14,20 +14,9 @@ in
         Amount of free space (GB) to ensure on garbage collection
       '';
     };
-    freespaceMinimumGB = mkOption {
-      type = types.nullOr types.int;
-      default = 10;
-      description = ''
-        Amount of free space (GB) Nix will allow /nix/store to drop to before GC-ing.
-      '';
-    };
   };
 
   config = mkIf (cfg.enable && cfg.freespaceGB != null) {
-    nix.extraOptions = ''
-      min-free = ${toString (1024 * 1024 * 1024 * cfg.freespaceMinimumGB)}
-      max-free = ${toString (1024 * 1024 * 1024 * cfg.freespaceGB)}
-    '';
     nix.gc.automatic = true;
     nix.gc.options = ''--max-freed "$((${toString cfg.freespaceGB} * 1024**3 - 1024 * $(df -P -k /nix/store | tail -n 1 | ${pkgs.gawk}/bin/awk '{ print $4 }')))"'';
   };