fix bug with bootstrap form theme textarea (horizontal layout mode)

cfr issue https://gitlab.com/champs-libres/departement-de-la-vendee/chill/-/issues/182
+ make chill fields theme more responsive

src/Bundle/ChillEventBundle/Resources/views/Event/listByPerson.html.twig

@@ -108,8 +108,6 @@
     {{ chill_pagination(paginator) }}
 {% endif %}
 
-{% form_theme form_add_event_participation_by_person 'bootstrap_4_layout.html.twig' %}
-
 <div class="input-group mb-3">
 {{ form_start(form_add_event_participation_by_person) }}
     {#
@@ -137,4 +135,4 @@
     </div>
 </div>
 
-{% endblock %}
+{% endblock %}