Remove fomantic checkbox module (#30162) (#30168)

Remove fomantic checkbox module (#30162) (#30168)

Backport #30162 by @silverwind

CSS is pretty slim already and the `.ui.toggle.checkbox` sliders on
admin page also still work. The only necessary JS is the one that links
`input` and `label` so that it can be toggled via label. All checkboxes
except the markdown ones render at `--checkbox-size: 16px` now.

<img width="174" alt="Screenshot 2024-03-28 at 22 15 10"
src="https://github.com/go-gitea/gitea/assets/115237/3455c1bb-166b-47e4-9847-2d20dd1f04db">

<img width="499" alt="Screenshot 2024-03-28 at 21 00 07"
src="https://github.com/go-gitea/gitea/assets/115237/412be2b3-d5a0-478a-b17b-43e6bc12e8ce">

<img width="83" alt="Screenshot 2024-03-28 at 22 14 34"
src="https://github.com/go-gitea/gitea/assets/115237/d8c89838-a420-4723-8c49-89405bb39474">

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: delvh <dev.lh@web.de>