Remove fomantic label module (#30081)

Of note is the CSS has references to "floating label" and "transparent
label" but I could not find those anywhere in the code. They are related
to https://github.com/go-gitea/gitea/pull/3939, but I think these have
long been removed.

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Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Giteabot <teabot@gitea.io>

web_src/fomantic/semantic.json

@@ -28,7 +28,6 @@
     "dropdown",
     "form",
     "input",
-    "label",
     "list",
     "menu",
     "modal",