ant: rip out ant-contrib

nixpkgs-review reveals no new failures when we remove this,
so let's rip it out per the rationale at #357758.

Closes #357758.

nixos/doc/manual/release-notes/rl-2511.section.md

···
 - `libvirt` now supports using `nftables` backend.
   - The `virtualisation.libvirtd.firewallBackend` option can be used to configure the firewall backend used by libvirtd.
 
+- The third-party `ant-contrib` is no longer included in the `ant` package.
+
 - `systemd.extraConfig` and `boot.initrd.systemd.extraConfig` was converted to RFC42-style `systemd.settings.Manager` and `boot.initrd.systemd.settings.Manager` respectively.
   - `systemd.watchdog.runtimeTime` was renamed to `systemd.settings.Manager.RuntimeWatchdogSec`
   - `systemd.watchdog.device` was renamed to `systemd.settings.Manager.WatchdogDevice`

pkgs/by-name/an/ant/package.nix

···
     hash = "sha256-h/SNGLoRwRVojDfvl1g+xv+J6mAz+J2BimckjaRxDEs=";
   };
 
-  contrib = fetchurl {
-    url = "mirror://sourceforge/ant-contrib/ant-contrib-1.0b3-bin.tar.bz2";
-    sha256 = "1l8say86bz9gxp4yy777z7nm4j6m905pg342li1aphc14p5grvwn";
-  };
-
   installPhase = ''
     mkdir -p $out/bin $out/share/ant
     mv * $out/share/ant/
···
     rm -rf $out/share/ant/{manual,bin,WHATSNEW}
     mkdir $out/share/ant/bin
     mv $out/bin/antRun $out/share/ant/bin/
-
-    # Install ant-contrib.
-    unpackFile $contrib
-    cp -p ant-contrib/ant-contrib-*.jar $out/share/ant/lib/
 
     cat >> $out/bin/ant <<EOF
     #! ${stdenv.shell} -e