Simplify calls to content_block helper

All calls were using `I18n.locale` as the second parameter, so we might
as well make it optional.

app/components/layout/social_component.rb

@@ -26,6 +26,6 @@ class Layout::SocialComponent < ApplicationComponent
     end
 
     def footer_content_block
-      content_block("footer", I18n.locale)
+      content_block("footer")
     end
 end

app/components/layout/top_links_component.rb

@@ -8,6 +8,6 @@ class Layout::TopLinksComponent < ApplicationComponent
   private
 
     def top_links_content_block
-      content_block("top_links", I18n.locale)
+      content_block("top_links")
     end
 end

app/helpers/application_helper.rb

@@ -48,7 +48,7 @@ module ApplicationHelper
     SiteCustomization::Image.image_path_for(filename) || filename
   end
 
-  def content_block(name, locale)
+  def content_block(name, locale = I18n.locale)
     SiteCustomization::ContentBlock.block_for(name, locale)
   end
 

app/views/shared/_subnavigation.html.erb

@@ -1,6 +1,6 @@
 <div class="small-12 medium-9 column">
   <ul>
-    <%= raw content_block("subnavigation_left", I18n.locale) %>
+    <%= raw content_block("subnavigation_left") %>
 
     <% if feature?(:debates) %>
       <li>
@@ -59,6 +59,6 @@
       </li>
     <% end %>
 
-    <%= raw content_block("subnavigation_right", I18n.locale) %>
+    <%= raw content_block("subnavigation_right") %>
   </ul>
 </div>