buildbot: Remove broken on Darwin.

It seems to me that buildbot is not broken on Darwin.

This build failure was referenced from a comment: https://hydra.nixos.org/build/243534318/nixlog/6.

I was able to successfully build, run and get a basic buildbot master, worker
and web ui going on my aarch64-darwin machine:

```
❯ nix run .#nix-info -- -m
 - system: `"aarch64-darwin"`
 - host os: `Darwin 24.0.0, macOS 15.0.1`
 - multi-user?: `no`
 - sandbox: `yes`
 - version: `nix-env (Lix, like Nix) 2.91.1
System type: aarch64-darwin
Additional system types:
Features: gc, signed-caches
System configuration file: /etc/nix/nix.conf
User configuration files: /Users/andreas/.config/nix/nix.conf:/etc/xdg/nix/nix.conf
Store directory: /nix/store
State directory: /nix/var/nix
Data directory: /nix/store/1phn7b1smb3g9jqz7v39q13wlyji2msz-lix-2.91.1/share`
 - nixpkgs: `not found`

❯ nix build .#buildbot-full
❯ result/bin/buildbot create-master /tmp/my_master
mkdir /tmp/my_master
creating /tmp/my_master/master.cfg.sample
creating database (sqlite:///state.sqlite)
buildmaster configured in /tmp/my_master
❯ mv /tmp/my_master/master.cfg.sample /tmp/my_master/master.cfg
❯ result/bin/buildbot start /tmp/my_master
Following twistd.log until startup finished..
The buildmaster appears to have (re)started correctly.

❯ nix build .#buildbot-worker
❯ result/bin/buildbot-worker create-worker /tmp/my_worker localhost example-worker pass
mkdir /tmp/my_worker
mkdir /tmp/my_worker/info
Creating info/admin, you need to edit it appropriately.
Creating info/host, you need to edit it appropriately.
Not creating info/access_uri - add it if you wish
Please edit the files in /tmp/my_worker/info appropriately.
worker configured in /tmp/my_worker
❯ result/bin/buildbot-worker start /tmp/my_worker
Following twistd.log until startup finished..
The buildbot-worker appears to have (re)started correctly.
```

pkgs/development/tools/continuous-integration/buildbot/master.nix

@@ -176,6 +176,5 @@ buildPythonApplication rec {
     changelog = "https://github.com/buildbot/buildbot/releases/tag/v${version}";
     maintainers = teams.buildbot.members;
     license = licenses.gpl2Only;
-    broken = stdenv.hostPlatform.isDarwin;
   };
 }

pkgs/development/tools/continuous-integration/buildbot/worker.nix

@@ -56,6 +56,5 @@ buildPythonPackage ({
     description = "Buildbot Worker Daemon";
     maintainers = teams.buildbot.members;
     license = licenses.gpl2;
-    broken = stdenv.hostPlatform.isDarwin; # https://hydra.nixos.org/build/243534318/nixlog/6
   };
 })