Remove fomantic transition module (#26469)

Removes all dropdown and dimmer animations. Works everywhere as far as I
can tell, but need to give this thorough testing. Removes around 70kb
JS/CSS.

Note, I'm not 100% sure regarding the various callbacks, those will need
more investigation, but it appears to work nonetheless.

Fixes: https://github.com/go-gitea/gitea/issues/15709

web_src/css/themes/theme-arc-green.css

@@ -233,6 +233,7 @@
   --color-accent: var(--color-primary-light-1);
   --color-small-accent: var(--color-primary-light-5);
   --color-active-line: #534d1b;
+  --color-overlay-backdrop: #080808c0;
   accent-color: var(--color-accent);
   color-scheme: dark;
 }