fix exception in LMS when rendering newly create multiple choice problems. The…

fix exception in LMS when rendering newly create multiple choice problems. The capa module is barfing on the HTML comment which was in there and the XML parser couldn't handle it.

common/lib/xmodule/xmodule/templates/problem/multiplechoice.yaml

@@ -8,7 +8,7 @@ data: |
  
  <p>
    A multiple choice response problem presents radio buttons for student 
-   input.  <!-->One or more of the choice may be correct.-->  Correctness of
+   input. Correctness of
    input is evaluated based on expected answers specified within each
    "choice" stanza.
  </p>