Remove ISSUE label about ms

Consensus from 2019/11/11 was to keep it in core as a mn-like
element. Which is what the spec currently says.

w3c/mathml#120

Author: fred-wang

index.html

@@ -257,7 +257,6 @@ <h3>XML</h3>
           <h4>HTML and SVG</h4>
           <div class="issue" data-number="103">mpadded?</div>
           <div class="issue" data-number="105">menclose?</div>
-          <div class="issue" data-number="120">ms?</div>
           <div class="issue" data-number="25">mglyph?</div>
           <div class="issue" data-number="72">mlabeledtr?</div>
           <p>