Support selecting theme on the footer (#35741)

Fixes: https://github.com/go-gitea/gitea/pull/27576

modules/templates/helper.go

@@ -12,7 +12,6 @@ import (
 	"strings"
 	"time"
 
-	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/htmlutil"
 	"code.gitea.io/gitea/modules/markup"
@@ -21,7 +20,6 @@ import (
 	"code.gitea.io/gitea/modules/templates/eval"
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/services/gitdiff"
-	"code.gitea.io/gitea/services/webtheme"
 )
 
 // NewFuncMap returns functions for injecting to templates
@@ -130,7 +128,6 @@ func NewFuncMap() template.FuncMap {
 		"DisableWebhooks": func() bool {
 			return setting.DisableWebhooks
 		},
-		"UserThemeName": userThemeName,
 		"NotificationSettings": func() map[string]any {
 			return map[string]any{
 				"MinTimeout":            int(setting.UI.Notification.MinTimeout / time.Millisecond),
@@ -217,16 +214,6 @@ func evalTokens(tokens ...any) (any, error) {
 	return n.Value, err
 }
 
-func userThemeName(user *user_model.User) string {
-	if user == nil || user.Theme == "" {
-		return setting.UI.DefaultTheme
-	}
-	if webtheme.IsThemeAvailable(user.Theme) {
-		return user.Theme
-	}
-	return setting.UI.DefaultTheme
-}
-
 func isQueryParamEmpty(v any) bool {
 	return v == nil || v == false || v == 0 || v == int64(0) || v == ""
 }