Fix phase banner left/right spacing on some pages

- below the tablet breakpoint (around 1020px) the phase banner at the top of some pages was being padded left and right, which indented it from the rest of the page
- caused by the govuk-frontend grid wrapping classes, which were unnecessary
- some wrapping divs moved instead to support the phase label, which is similar but does require additional wrapping elements

app/views/layouts/application.html.erb

@@ -6,18 +6,12 @@
 
 <% content_for :body do %>
   <div id="wrapper" class="<%= wrapper_class %>">
-    <% if @content_item.show_phase_banner? || @content_item.service_manual? %>
+    <% if @content_item.show_phase_banner? %>
+      <%= render 'govuk_publishing_components/components/phase_banner', phase: @content_item.phase %>
+    <% end %>
+    <% if @content_item.service_manual? %>
       <div class="govuk-width-container">
-        <div class="govuk-grid-row">
-          <div class="govuk-grid-column-full">
-            <% if @content_item.show_phase_banner? %>
-              <%= render 'govuk_publishing_components/components/phase_banner', phase: @content_item.phase %>
-            <% end %>
-            <% if @content_item.service_manual? %>
-              <%= render_phase_label @content_item, content_for(:phase_message) %>
-            <% end %>
-          </div>
-        </div>
+        <%= render_phase_label @content_item, content_for(:phase_message) %>
       </div>
     <% end %>