Remove unused partial

It isn't used since commit 5d37997a6, when it was replaced with the
`debate.html.erb` template.

app/views/legislation/processes/_debate.html.erb

@@ -1,17 +0,0 @@
-<div class="small-12 medium-9 column">
-  <div class="debate-list">
-    <% if process.questions.empty? %>
-      <p><%= t("legislation.processes.debate.empty_questions") %></p>
-    <% else %>
-      <%= render process.questions %>
-    <% end %>
-  </div>
-</div>
-
-<% if process.questions.any? %>
-  <div class="small-12 medium-3 column">
-    <div class="callout success">
-      <p><%= t("legislation.processes.debate.participate") %></p>
-    </div>
-  </div>
-<% end %>