fix(ci-broker.md): drop unused embedded file — radicle-ci-broker

Unused files make subplot docgen fail unless it’s given the --merciful option.

Signed-off-by: Lars Wirzenius liw@liw.fi

       - !Branch "main"
 ~~~
 ~~~{#broker-allow-nothing.yaml .file .yaml}
 db: ci-broker.db
 report_dir: reports
 default_adapter: mcadapterface
 adapters:
   mcadapterface:
     command: ./adapter.sh
     env:
       RADICLE_NATIVE_CI: native-ci.yaml
     sensitive_env: {}
 filters:
   - !Branch "this-branch-does-not-exist"
 ~~~
 ## A dummy adapter