.github/workflows: delete CIFuzz job
It doesn't yet support Go 1.20. We can bring it back later.
Updates
name: CIFuzz
-on: [pull_request]
+on: [] # was: [pull_request], but disabled in https://github.com/tailscale/tailscale/pull/7156
concurrency:
group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
