Remove unused audit-ci dependency

There is a `yarn ci` script which was using audit-ci but this does not
appear to be called anywhere.

The security worflow uses `yarn audit` and `npm audit` which seem fine
enough anyway.

.github/workflows/security.yaml

@@ -19,7 +19,7 @@ concurrency:
   cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
-  audit-ci:
+  audit:
     name: Audit node modules
     runs-on: ubuntu-latest
     timeout-minutes: 15