Remove audit workflow

It is not really useful. cg_clif is meant for development only and has
relatively few dependencies. It has only ever caught an unmaintained
crate about which nothing could be done on our end as cranelift-jit
depended on it.

.github/workflows/audit.yml

@@ -1,18 +0,0 @@
-name: Security audit
-on:
-  workflow_dispatch:
-  schedule:
-    - cron: '0 10 * * 1' # every monday at 10:00 UTC
-permissions:
-  issues: write
-  checks: write
-jobs:
-  audit:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - run: |
-          sed -i 's/components.*/components = []/' rust-toolchain.toml
-      - uses: rustsec/audit-check@v2.0.0
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}