Remove heading helper from search component

- not used
- also remove it from the auditing tools, because it's only used by one other component (the heading component) and we only need to audit helpers that are used by multiple components, lots of components already have their own individual helpers

app/models/govuk_publishing_components/audit_components.rb

@@ -262,12 +262,6 @@ def get_helper_usage(components)
           match: /(GovukPublishingComponents::Presenters::ComponentWrapperHelper.new)/,
           used_by: [],
         },
-        {
-          name: "Heading helper",
-          link: "lib/govuk_publishing_components/presenters/heading_helper.rb",
-          match: /(GovukPublishingComponents::Presenters::HeadingHelper.new)/,
-          used_by: [],
-        },
         {
           name: "Shared helper",
           link: "lib/govuk_publishing_components/presenters/shared_helper.rb",

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

@@ -3,7 +3,6 @@
   add_gem_component_stylesheet("label")
 
   shared_helper = GovukPublishingComponents::Presenters::SharedHelper.new(local_assigns)
-  heading_helper = GovukPublishingComponents::Presenters::HeadingHelper.new(local_assigns)
 
   aria_controls ||= nil
   button_text ||= t("components.search_box.search_button")

spec/component_guide/audit_components_spec.rb

@@ -104,12 +104,6 @@
             },
           ],
         },
-        {
-          link: "lib/govuk_publishing_components/presenters/heading_helper.rb",
-          match: /(GovukPublishingComponents::Presenters::HeadingHelper.new)/,
-          name: "Heading helper",
-          used_by: [],
-        },
         {
           link: "lib/govuk_publishing_components/presenters/shared_helper.rb",
           match: /(GovukPublishingComponents::Presenters::SharedHelper.new)/,