Fix dropdown icon layout on diff page (#25397) (#25403)

Backport #25397 by @wxiaoguang

Address
https://github.com/go-gitea/gitea/pull/25163#issuecomment-1599207916

Remove the unused  "icon-button".

And fix the layout:

Without the dropdown icon:

```
	{{svg "gitea-whitespace"}}
```


![image](https://github.com/go-gitea/gitea/assets/2114189/58a524ba-f289-4982-aea2-6f9f9f9cbdcf)


With the dropdown icon:

```
	{{svg "gitea-whitespace" 16 "gt-mr-3"}}
	{{svg "octicon-triangle-down" 14 "dropdown icon"}}
```


![image](https://github.com/go-gitea/gitea/assets/2114189/eb99168b-5d49-40a7-8665-5296cbb4e486)

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/package/shared/cleanup_rules/list.tmpl

@@ -9,7 +9,7 @@
 		{{range .CleanupRules}}
 			<div class="item">
 				<div class="right floated content">
-					<div class="ui dropdown tiny basic button icon-button">
+					<div class="ui dropdown tiny basic button">
 						{{svg "octicon-kebab-horizontal"}}
 						<div class="menu">
 							<a class="item" href="{{$.Link}}/rules/{{.ID}}">{{$.locale.Tr "edit"}}</a>