Remove title component margin_top option

- our spacing model is to apply margin bottom, so this is an anomaly
- replace margin_top with default padding on the component, so no visual changes
- margin_top option isn't widely used and can be replaced with alternatives, separate PRs will be raised

app/assets/stylesheets/govuk_publishing_components/components/_title.scss

@@ -1,5 +1,11 @@
 @import "govuk_publishing_components/individual_component_support";
 
+.gem-c-title {
+  @include govuk-media-query($from: tablet) {
+    padding-top: govuk-spacing(8);
+  }
+}
+
 .gem-c-title--inverse {
   color: govuk-colour("white");
 

app/views/govuk_publishing_components/components/_title.html.erb

@@ -8,20 +8,17 @@
   context_inside ||= false
 
   inverse ||= false
-  local_assigns[:margin_top] ||= 8
   local_assigns[:margin_bottom] ||= 8
 
   shared_helper = GovukPublishingComponents::Presenters::SharedHelper.new(local_assigns)
 
   classes = %w[gem-c-title]
   classes << "gem-c-title--inverse" if inverse
-  classes << shared_helper.get_margin_top
   classes << shared_helper.get_margin_bottom
 
   heading_classes = %w[gem-c-title__text]
   heading_classes << (average_title_length.present? ? 'govuk-heading-l' : 'govuk-heading-xl')
 %>
-
 <% @context_block = capture do %>
   <span class="govuk-caption-xl gem-c-title__context" <%= "lang=#{context_locale}" if context_locale.present? %>>
     <%= context %>

spec/components/title_spec.rb

@@ -71,26 +71,6 @@ def component_name
     assert_select "[class^='govuk-\!-margin-bottom-']", false
   end
 
-  it "has a default margin top of 8" do
-    render_component(title: "Margin default")
-    assert_select '.gem-c-title.govuk-\!-margin-top-8'
-  end
-
-  it "applies a margin top of 0" do
-    render_component(title: "Margin 0", margin_top: 0)
-    assert_select '.gem-c-title.govuk-\!-margin-top-0'
-  end
-
-  it "applies a valid margin top" do
-    render_component(title: "Margin 4", margin_top: 4)
-    assert_select '.gem-c-title.govuk-\!-margin-top-4'
-  end
-
-  it "ignores an invalid margin top" do
-    render_component(title: "Margin wat", margin_top: 17)
-    assert_select "[class^='govuk-\!-margin-top-']", false
-  end
-
   it "applies context language if supplied to a context link" do
     render_component(title: "Bonjour", context: "Format", context_locale: "en")
     assert_select ".govuk-caption-xl[lang='en']"