fix: convert cf-kv and excalidraw-libraries from submodules to regular files

- Remove stale cloudflare-worker submodule entry from .gitmodules
- Remove .git dirs from cf-kv and excalidraw-libraries so Git tracks them as regular files
- Fixes 'No url found for submodule path cf-kv' CI error

excalidraw-libraries/.github/workflows/validate-libraries.yml

@@ -0,0 +1,17 @@
+name: Validate libraries.json
+
+on: pull_request
+
+jobs:
+  validation:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Setup Node.js 14.x
+        uses: actions/setup-node@v2
+        with:
+          node-version: 14.x
+      - name: Validate libraries.json
+        run: |
+          yarn validate:libraries