chore(ui): remove ineffective class small in inline code preview (#7414)
Followup to https://codeberg.org/forgejo/forgejo/pulls/2669
Ref https://codeberg.org/forgejo/forgejo/issues/5067
Since Forgejo v9 this class is overridden here by other CSS and is ineffective. But it looks ok and gives good visibility. If it needs to be re-implemed, it can be done via CSS, like:
```css
.file-preview-box .header span {font-size:0.8rem;}
```
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7414
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: 0ko <0ko@noreply.codeberg.org>
Co-committed-by: 0ko <0ko@noreply.codeberg.org>