R: unpin JDK

JDK was pinned at JDK 8, causing stalling issues with downstream
rPackages (rJava and dependees).

pkgs/top-level/all-packages.nix

@@ -21380,7 +21380,6 @@ with pkgs;
     withRecommendedPackages = false;
     inherit (darwin.apple_sdk.frameworks) Cocoa Foundation;
     inherit (darwin) libobjc;
-    jdk = jdk8; # TODO: remove override https://github.com/NixOS/nixpkgs/pull/89731
   };
 
   rWrapper = callPackage ../development/r-modules/wrapper.nix {