Revert "Merge #255483: krb5: 1.20.1 -> 1.21.2"
This reverts commit d82971922624968c273fbf972323327144c0e400, reversing
changes made to 93c0a7c19668da4e208f043e4673acb7c1b30fce.
Some packages started missing kerberos framework on darwin.
https://github.com/NixOS/nixpkgs/pull/255483#issuecomment-1747218729
https://hydra.nixos.org/build/237078859/nixlog/5/tail
So for now we'll do a patch-level bump instead to fix security issues.