Remove fomantic message module (#29856)

Remove this CSS-only module, which gives a nice reduction in CSS size.
Should look exactly like before.

web_src/css/index.css

@@ -12,6 +12,7 @@
 @import "./modules/divider.css";
 @import "./modules/svg.css";
 @import "./modules/flexcontainer.css";
+@import "./modules/message.css";
 
 @import "./shared/flex-list.css";
 @import "./shared/milestone.css";