dashboard: remove the unused bootstrap-icons.css

We should revisit this later because it's a lot simpler for people
to just include the CSS than copy around tens of icons, even if it
leads to unused CSS

site/content/docs/5.3/examples/dashboard/index.html

@@ -2,7 +2,6 @@
 layout: examples
 title: Dashboard Template
 extra_css:
-  - "https://cdn.jsdelivr.net/npm/bootstrap-icons@1.10.5/font/bootstrap-icons.min.css"
   - "dashboard.css"
 extra_js:
   - src: "https://cdn.jsdelivr.net/npm/chart.js@4.3.2/dist/chart.umd.js"