Remove GOVUK Template files

Includes Sass that targeted GOV.UK Template HTML
and also moves some link styles to `globals.scss`.

Also removes bits of frontend build that copied
over GOVUK Template files.

app/assets/stylesheets/app.scss

@@ -1,62 +1,4 @@
 // Extra CSS overlaying elements
-
-#global-header-bar {
-  background-color: $govuk-blue;
-}
-
-#global-header,
-#global-header.with-proposition {
-
-  #logo {
-
-    white-space: nowrap;
-
-    #product-name {
-      font-size: 24px;
-      font-weight: 400;
-      padding-left: 5px;
-    }
-
-  }
-
-  .header-wrapper {
-    .header-global {
-      .header-logo {
-
-        @include media(desktop) {
-          width: auto;
-        }
-
-        &:after {
-          display: none;
-        }
-
-      }
-    }
-  }
-
-  .header-proposition {
-    #proposition-links {
-      li {
-        padding: 0 0 0 15px;
-      }
-    }
-  }
-
-}
-
-@include media(desktop) {
-  #proposition-menu {
-    float: right;
-  }
-}
-
-a {
-  &:visited {
-    color: $link-colour;
-  }
-}
-
 .form-control-1-1 {
   width: 100%;
 }

app/assets/stylesheets/globals.scss

@@ -43,6 +43,12 @@ input[type="search"]::-webkit-search-decoration {
 // https://design-system.service.gov.uk/styles/typography/#links
 a {
   @extend %govuk-link;
+
+  // Stops visited links looking different, until we can add the `govuk-link--no-visited-state`
+  // class to all links we want stay the same colour after visiting
+  &:visited {
+    color: $govuk-link-colour;
+  }
 }
 
 // Each selector, and then the whole block when only one remains, to be removed when the