Update media-alternative-prerecorded.html

Only one note exists in 1.2.8; however, it contains multiple paragraphs which are enumerated as separate notes in 1.2.3 and 1.2.5.
The first paragraph of 1.2.8, which corresponds to note 1 in 1.2.3 and 1.2.5, is irrelevant to 1.2.8.
By removing this paragraph, 1.2.8 is reduced to coverrng a single concept, which results in an unnumbered note, by convention.

Author: mbgower

understanding/20/media-alternative-prerecorded.html

@@ -56,13 +56,6 @@ Intent of Media Alternative (Prerecorded)
 
       <div class="note">
 
-         <p>
-            For 1.2.3, 1.2.5, and 1.2.7, if all of the information in the video track is already
-            provided in the audio track, no audio description is necessary. 
-            
-            
-         p>
-         
          <p>
             1.2.3, 1.2.5, and 1.2.8 overlap somewhat with each other. This is to give the author
             some choice at the minimum conformance level, and to provide additional requirements