Remove Advisory component

The advisory component has been earmarked for removal.
It does not pull in styles from the design system and so has to be
manually updated if it needs changing.
'Information callouts' will be used instead.

README.md

@@ -81,18 +81,6 @@ creates an example box
 
 ## Highlights
 
-### Advisory (DEPRECATED: marked for removal. Use 'Information callouts' instead.)
-
-    @This is a very important message or warning@
-
-highlights the enclosed text in yellow
-
-```html
-<h3 role="note" aria-label="Important" class="advisory">
-  <span>This is a very important message or warning</span>
-</h3>
-```
-
 ### Answer (DEPRECATED: marked for removal)
 
     {::highlight-answer}

lib/govspeak.rb

@@ -201,10 +201,6 @@ def insert_strong_inside_p(body, parser = Govspeak::Document)
 #{Govspeak::Document.new(body.strip).to_html}</div>\n)
     end
 
-    extension("important", surrounded_by("@")) do |body|
-      %(\n\n<div role="note" aria-label="Important" class="advisory">#{insert_strong_inside_p(body)}</div>\n)
-    end
-
     extension("helpful", surrounded_by("%")) do |body|
       %(\n\n<div role="note" aria-label="Warning" class="application-notice help-notice">\n#{Govspeak::Document.new(body.strip).to_html}</div>\n)
     end

test/govspeak_test.rb

@@ -176,27 +176,6 @@ class GovspeakTest < Minitest::Test
     assert_text_output "I am very informational"
   end
 
-  test_given_govspeak "@ I am very important @" do
-    assert_html_output %(
-      <div role="note" aria-label="Important" class="advisory">
-      <p><strong>I am very important</strong></p>
-      </div>)
-    assert_text_output "I am very important"
-  end
-
-  test_given_govspeak "
-    The following is very important
-    @ I am very important @
-    " do
-    assert_html_output %(
-      <p>The following is very important</p>
-
-      <div role="note" aria-label="Important" class="advisory">
-      <p><strong>I am very important</strong></p>
-      </div>)
-    assert_text_output "The following is very important I am very important"
-  end
-
   test_given_govspeak "% I am very helpful %" do
     assert_html_output %(
       <div role="note" aria-label="Warning" class="application-notice help-notice">
@@ -1478,14 +1457,6 @@ class GovspeakTest < Minitest::Test
       '
   end
 
-  test_given_govspeak "@ Message with [a link](http://foo.bar/)@" do
-    assert_html_output %(
-      <div role="note" aria-label="Important" class="advisory">
-      <p><strong>Message with <a rel="external" href="http://foo.bar/">a link</a></strong></p>
-      </div>
-      )
-  end
-
   test "sanitize source input by default" do
     document = Govspeak::Document.new("<script>doBadThings();</script>")
     assert_equal "", document.to_html.strip