ci: remove redundant .nojekyll creation and clean up CNAME

- Replace touch build/.nojekyll with rm -f build/CNAME in smalruby3-gui
  GitHub Pages deployment step
- .nojekyll already exists from smalruby.app deployment since they share
  the same build directory
- Remove CNAME file created for smalruby.app to prevent domain conflicts
  with smalruby3-gui GitHub Pages

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: takaokouji

.github/workflows/ci-cd.yml

@@ -125,7 +125,7 @@ jobs:
               run: npm exec node ./scripts/postbuild.mjs
             - name: Prepare deployment files for smalruby3-gui GitHub Pages
               if: github.ref == 'refs/heads/develop' || github.ref == 'refs/heads/master' || github.ref == 'refs/heads/main'
-              run: touch build/.nojekyll
+              run: rm -f build/CNAME
             - name: Deploy playground to GitHub Pages
               uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3
               if: github.ref == 'refs/heads/develop' || github.ref == 'refs/heads/master' || github.ref == 'refs/heads/main'