GH-actions: remove CIFuzz workflow

The CIFuzz tool was observed detecting an issue in code unrelated to a
pull request. While it was relatively benign in this case, it has the
potential to accidentally disclose a vulnerability publicly without
allowing a non-disclosure period for us to publish a fixed patch
version.

I'm not comfortable with this risk, so I'm removing the workflow.

.github/workflows/cifuzz.yml

@@ -1,24 +0,0 @@
-name: CIFuzz
-on: [pull_request]
-jobs:
-  Fuzzing:
-    runs-on: ubuntu-latest
-    steps:
-    - name: Build Fuzzers
-      id: build
-      uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
-      with:
-        oss-fuzz-project-name: 'clamav'
-        dry-run: false
-    - name: Run Fuzzers
-      uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
-      with:
-        oss-fuzz-project-name: 'clamav'
-        fuzz-seconds: 600
-        dry-run: false
-    - name: Upload Crash
-      uses: actions/upload-artifact@v1
-      if: failure() && steps.build.outcome == 'success'
-      with:
-        name: artifacts
-        path: ./out/artifacts