referencesByPopularity: Don't use buildPackages at call-site

It's cleaner to reference buildPackages directly in
build-support/docker directly.

pkgs/build-support/docker/default.nix

@@ -15,7 +15,6 @@
   moreutils,
   nix,
   pigz,
-  referencesByPopularity,
   rsync,
   runCommand,
   runtimeShell,
@@ -772,7 +771,7 @@ rec {
             then tag
             else
               lib.head (lib.strings.splitString "-" (baseNameOf conf.outPath));
-        paths = referencesByPopularity overallClosure;
+        paths = buildPackages.referencesByPopularity overallClosure;
         nativeBuildInputs = [ jq ];
       } ''
         ${if (tag == null) then ''

pkgs/top-level/all-packages.nix

@@ -511,7 +511,7 @@ in
 
   nukeReferences = callPackage ../build-support/nuke-references { };
 
-  referencesByPopularity = buildPackages.callPackage ../build-support/references-by-popularity { };
+  referencesByPopularity = callPackage ../build-support/references-by-popularity { };
 
   removeReferencesTo = callPackage ../build-support/remove-references-to { };