remove dead link to an RNIB blog (#4255)

I tried to find it on the wayback machine, but couldn't.

Also: I was quite tempted to remove the link to the NNG group's article
on using the title attribute.

---------

Co-authored-by: Mike Gower <mikegower@gmail.com>

Author: fstrr

understanding/20/link-purpose-in-context.html

@@ -156,27 +156,13 @@ <h2>Examples of Link Purpose (In Context)</h2>
    <section id="resources">
       <h2>Resources for Link Purpose (In Context)</h2>
 
-      
       <ul>
-         
-         <li>
-            								       
-            <a href="https://www.nngroup.com/articles/using-link-titles-to-help-users-predict-where-they-are-going/">Using Link Titles to Help Users Predict Where They Are Going</a>
-            							     
-         </li>
-         
-         <li>
-            								       
-            <a href="http://webaim.org/techniques/hypertext/">WebAIM Techniques for Hypertext Links</a>
-            							     
+         <li>			       
+            <a href="https://www.nngroup.com/articles/using-link-titles-to-help-users-predict-where-they-are-going/">Using Link Titles to Help Users Predict Where They Are Going</a>						     
          </li>
-         
          <li>
-            	
-            <a href="http://www.rnib.org.uk/blogs/expert-series?Name=Hidden%20barriers">Hidden barriers - out of sight</a>
-            							     
+            <a href="http://webaim.org/techniques/hypertext/">WebAIM Techniques for Hypertext Links</a>						     
          </li>
-         
       </ul>
 
    </section>

understanding/20/link-purpose-link-only.html

@@ -127,25 +127,12 @@ <h2>Resources for Link Purpose (Link Only)</h2>
 
 
       <ul>
-         
          <li>
-            								       
-            <a href="https://www.nngroup.com/articles/using-link-titles-to-help-users-predict-where-they-are-going/">Using Link Titles to Help Users Predict Where They Are Going</a>
-            							     
+            <a href="https://www.nngroup.com/articles/using-link-titles-to-help-users-predict-where-they-are-going/">Using Link Titles to Help Users Predict Where They Are Going</a>						     
          </li>
-         
-         <li>
-            								       
-            <a href="http://webaim.org/techniques/hypertext/">WebAIM Techniques for Hypertext Links</a>
-            							     
+         <li>							       
+            <a href="http://webaim.org/techniques/hypertext/">WebAIM Techniques for Hypertext Links</a>						     
          </li>
-         
-         <li>
-            	
-            <a href="http://www.rnib.org.uk/blogs/expert-series?Name=Hidden%20barriers">Hidden barriers - out of sight</a>
-            							     
-         </li>
-         
       </ul>
 
    </section>