Remove Quarto 1.4 pre-release callout

As Quarto 1.4 is released, the pre-release callout on the Dashboard documentation page can be removed.

docs/dashboards/index.qmd

@@ -16,8 +16,6 @@ format:
         </script>   
 ---
 
-{{< include /docs/prerelease/1.4/_pre-release-feature.qmd >}}
-
 ## Overview
 
 Quarto Dashboards make it easy to create interactive dashboards using Python, R, Julia, and Observable: