release.nix and release-small.nix: remove unar, fixes #76927

This package is hardly used in Nixpkgs. Why is it considered
sufficiently important to block a channel?

It's been blocking the nixpkgs-unstable for 8 days now, so removing it
from release*.nix.

pkgs/top-level/release-small.nix

@@ -156,7 +156,6 @@ with import ./release-lib.nix { inherit supportedSystems; };
   time = linux;
   tinycc = linux;
   udev = linux;
-  unar = linux;
   unzip = all;
   usbutils = linux;
   utillinux = linux;

pkgs/top-level/release.nix

@@ -105,7 +105,6 @@ let
               jobs.nix-info-tested.x86_64-linux
               # Ensure that X11/GTK are in order.
               jobs.thunderbird.x86_64-linux
-              jobs.unar.x86_64-linux
               jobs.cachix.x86_64-linux
 
               /*