Set select2 width to 100% so they adapt when browser window is resized

With that style, all formset rows were a fix pixels less wide than surrounding content

src/pretix/static/pretixcontrol/js/ui/main.js

@@ -485,6 +485,7 @@ var form_handlers = function (el) {
             theme: "bootstrap",
             language: $("body").attr("data-select2-locale"),
             data: JSON.parse($(this.getAttribute('data-select2-src')).text()),
+            width: '100%',
         }).val(selectedValue).trigger('change');
     });
 

src/pretix/static/pretixcontrol/scss/_forms.scss

@@ -63,10 +63,6 @@ td > .form-group > .checkbox {
   @include box-shadow(none);
 }
 
-div[data-formset-body], div[data-formset-form], div[data-nested-formset-form], div[data-nested-formset-body], details[data-formset-form] {
-  width: 100%;
-}
-
 .form-plugins .panel-title {
   line-height: 34px;
 }