Remove blue bar layout and styles

Remove blue bar layout and styles from 'landing page'. Used by Plan for Change pages (https://www.gov.uk/missions)

app/assets/stylesheets/views/_landing_page.scss

@@ -3,11 +3,6 @@
 @import "_landing_page/helpers/backgrounds";
 @import "_landing_page/helpers/borders";
 
-.landing-page-header__blue-bar {
-  background-color: govuk-colour("blue");
-  height: govuk-spacing(2);
-}
-
 .landing-page-header__org {
   padding-top: govuk-spacing(2);
   padding-bottom: govuk-spacing(6);

app/assets/stylesheets/views/_landing_page/themes/prime-ministers-office-10-downing-street.scss

@@ -1,4 +1,7 @@
 .landing-page-header {
   // I've used the hex value for the background colour as it doesn't exist in the colour palette
   background-color: #231F20;
-}
+  // Setting the overflow to auto is required to prevent the breadcrumb
+  // component's margin from collapsing.
+  overflow: auto;
+}

app/views/landing_page/themes/_default.html.erb

@@ -1,9 +1,6 @@
 <% content_for :before_content do %>
 <div class="landing-page-header">
   <div class="govuk-width-container">
-    <div class="landing-page-header__blue-bar">
-    </div>
-
     <div class="govuk-!-margin-bottom-8">
       <%= yield :landing_page_breadcrumbs %>
     </div>

app/views/landing_page/themes/_prime-ministers-office-10-downing-street.html.erb

@@ -7,9 +7,6 @@
 <% content_for :before_content do %>
 <div class="landing-page-header">
   <div class="govuk-width-container">
-    <div class="landing-page-header__blue-bar">
-    </div>
-
     <% if @content_item.breadcrumbs.present? %>
       <%= render "govuk_publishing_components/components/breadcrumbs", {
         collapse_on_mobile: true,