Apply Rails/SafeNavigation in officing booth view

In commit 9329e4b6e, `try` was added because there was a case where this
partial was rendered and the `current_booth` method didn't exist.
However, that's no longer the case since commit d5c7858f6. Since then,
this partial is only rendered in the officing section, where the
`current_booth` method is defined.

So we can use the safe navigation operator instead of `try`.

app/views/layouts/_officing_booth.html.erb

@@ -1,5 +1,5 @@
 <% if current_user.poll_officer? %>
   <div id="officing-booth" class="callout info">
-    <%= t("admin.officing_booth.title", booth: try(:current_booth)&.location) %>
+    <%= t("admin.officing_booth.title", booth: current_booth&.location) %>
   </div>
 <% end %>