Improve Wiki TOC (#24137)

The old code has a lot of technical debts, eg: `repo/wiki/view.tmpl` /
`Iterate`

This PR improves the Wiki TOC display and improves the code.

---------

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

modules/templates/helper.go

@@ -171,13 +171,6 @@ func NewFuncMap() []template.FuncMap {
 			}
 			return false
 		},
-		"Iterate": func(arg interface{}) (items []int64) {
-			count, _ := util.ToInt64(arg)
-			for i := int64(0); i < count; i++ {
-				items = append(items, i)
-			}
-			return items
-		},
 
 		// -----------------------------------------------------------------
 		// setting