refactor: derive the bus escort from the travel date

src/Form/StaffingRuleType.php

@@ -40,10 +40,6 @@ class StaffingRuleType extends AbstractType
                 'label' => 'Guiding',
                 'required' => false,
             ])
-            ->add('busEscort', CheckboxType::class, [
-                'label' => 'Busbegleitung',
-                'required' => false,
-            ])
             ->add('enabled', CheckboxType::class, [
                 'label' => 'aktiv',
                 'help' => 'Nur aktive Zeilen legen Einsätze an; die Vorschau zeigt alle',