fix for #1289: make sure to delete removed entities in GModel during sync also...

fix for #1289: make sure to delete removed entities in GModel during sync also with unbindWithoutChecks(): otherwise if some tags are reused (because entities have previsously been removed before the unbind, but without a sync between the two operations) we would find the (wrong) original entities in the GModel.


(cherry picked from commit 72b91c25)