Remove no longer necessary row classes

These element had no columns inside and the row classes had only been
added to give them a maximum width. That's no longer necessary since now
the body has that maximum width.

app/components/widget/feeds/participation_component.html.erb

@@ -1,4 +1,4 @@
-<div class="row margin-bottom feeds-list feeds-participation">
+<div class="margin-bottom feeds-list feeds-participation">
   <% feeds.each do |feed| %>
     <% if feed_proposals?(feed) || feed_debates?(feed) %>
       <%= render Widget::Feeds::FeedComponent.new(feed) %>