[MM-57356] Make use of go1.21 features (#26620)

server/channels/utils/api.go

@@ -12,11 +12,11 @@ import (
 	"net/http"
 	"net/url"
 	"path"
+	"slices"
 	"strings"
 
 	"github.com/mattermost/mattermost/server/public/model"
 	"github.com/mattermost/mattermost/server/public/shared/i18n"
-	"github.com/mattermost/mattermost/server/public/utils"
 )
 
 func CheckOrigin(r *http.Request, allowedOrigins string) bool {
@@ -114,7 +114,7 @@ func RenderMobileAuthComplete(w http.ResponseWriter, redirectURL string) {
 func RenderMobileError(config *model.Config, w http.ResponseWriter, err *model.AppError, redirectURL string) {
 	var link = template.HTMLEscapeString(redirectURL)
 	u, redirectErr := url.Parse(redirectURL)
-	if redirectErr != nil || !utils.Contains(config.NativeAppSettings.AppCustomURLSchemes, u.Scheme) {
+	if redirectErr != nil || !slices.Contains(config.NativeAppSettings.AppCustomURLSchemes, u.Scheme) {
 		link = *config.ServiceSettings.SiteURL
 	}
 	RenderMobileMessage(w, `