fix: address hard html validation complaint (ietf-tools#6121)

Author: rjsparks

ietf/templates/doc/frontpage.html

@@ -11,7 +11,7 @@
     <div class="row">
         <div class="col-md-12">
             <div class="text-center p-5">
-                <div class="ietflogo mx-auto p-3" alt="IETF">
+                <div class="ietflogo mx-auto p-3">
                     {% include "logo.html" with org="ietf" only %}
                 </div>
                 {% if server_mode != "production" %}