Remove failure technique F87

Rationale: this is not *always* a failure. User agent/screen reader support has improved considerably since the technique was first devised, with most (all?) combinations now happily reading/announcing CSS-generated content.

Supersedes #2800 (which was having too many merge conflicts due to its age)

Closes #1554, closes #3781

techniques/index.html

@@ -48,6 +48,7 @@ <h1 id="title" class="title p-name">Techniques for WCAG 2.2</h1>
 			<h2>Change Log</h2>
 			<p>A list of new, removed or significantly updated techniques:</p>
 			<ol>
+				<li><time datetime="2024-05-04">4 May 2024</time>: Removed F87 Failure of Success Criterion 1.3.1 due to inserting non-decorative content by using :before and :after pseudo-elements and the 'content' property in CSS</li>
         <li><time datetime="2020-07-15">15 July 2020</time>: Removed Flash techniques.</li>
         <li><time datetime="2019-09-12">12 Sept 2019</time>: Added <a href="failures/F105">Failure of Success Criterion 2.5.1 due to providing functionality via a path-based gesture without simple pointer alternative</a></li>
         <li><time datetime="2019-09-12">12 Sept 2019</time>: Added <a href="failures/F106">Failure due to inability to deactivate motion actuation</a></li>

understanding/20/info-and-relationships.html

@@ -558,12 +558,6 @@ <h3>Failures for Info and Relationships</h3>
 
             </li>
 
-            <li>
-
-               <a href="../../techniques/failures/F87" class="failure"></a>
-
-            </li>
-
             <li>
 
                <a href="../../techniques/failures/F90" class="failure"></a>