chore: remove unused demo video env vars from homepage workflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Lum1104

.github/workflows/deploy-homepage.yml

@@ -39,9 +39,6 @@ jobs:
       - name: Build homepage
         working-directory: homepage
         run: pnpm build
-        env:
-          VITE_STRUCTURAL_VIDEO_URL: ${{ vars.DEMO_STRUCTURAL_VIDEO_URL }}
-          VITE_DOMAIN_VIDEO_URL: ${{ vars.DEMO_DOMAIN_VIDEO_URL }}
 
       - name: Build core
         run: pnpm --filter @understand-anything/core build