unparam lint (#16771)

* fixed: `identifier` is unused lint error

* make saveMultipleMembersT method saveMultipleMembers

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/user.go

@@ -1302,7 +1302,7 @@ func (a *App) UpdateUser(user *model.User, sendNotifications bool) (*model.User,
 
 		if userUpdate.New.Username != userUpdate.Old.Username {
 			a.Srv().Go(func() {
-				if err := a.Srv().EmailService.sendChangeUsernameEmail(userUpdate.Old.Username, userUpdate.New.Username, userUpdate.New.Email, userUpdate.New.Locale, a.GetSiteURL()); err != nil {
+				if err := a.Srv().EmailService.sendChangeUsernameEmail(userUpdate.New.Username, userUpdate.New.Email, userUpdate.New.Locale, a.GetSiteURL()); err != nil {
 					mlog.Error("Failed to send change username email", mlog.Err(err))
 				}
 			})