packages-config.nix: ignore haskellPackages.hs-mesos

This attribute will necessarily cause an evaluation failures without
aliases, but removing the reliance on aliases will remove the error
message for users trying to use this attribute. Thus we'll work around
this for now.

pkgs/top-level/packages-config.nix

@@ -13,7 +13,6 @@
       fdbPackages
       fusePackages
       gns3Packages
-      haskellPackages
       idrisPackages
       nodePackages
       nodePackages_latest
@@ -31,6 +30,15 @@
       zeroadPackages
     ;
 
+    haskellPackages = super.haskellPackages // {
+      # mesos, which this depends on, has been removed from nixpkgs. We are keeping
+      # the error message for now, so users will get an error message they can make
+      # sense of, but need to work around it here.
+      # TODO(@sternenseemann): remove this after branch-off of 22.05, along with the
+      # override in configuration-nix.nix
+      hs-mesos = null;
+    };
+
     # Make sure haskell.compiler is included, so alternative GHC versions show up,
     # but don't add haskell.packages.* since they contain the same packages (at
     # least by name) as haskellPackages.