[CSS21] figure caption should not mention caption margin collapsing

Sometime since CSS2.0, we removed the sentence from 17.4 that said:
  # Vertical margins collapse where the table box and caption box
  # touch.
  --http://www.w3.org/TR/1998/REC-CSS2-19980512/tables.html#q5

Between
http://www.w3.org/TR/2007/CR-CSS21-20070719/tables.html#model and
http://www.w3.org/TR/2009/CR-CSS2-20090423/tables.html#model we also
fixed the figure in that section so that the margins don't collapse.

But the *caption* of the figure still says the margins collapse:
  # Diagram of a table with a caption above it; the top margin of
  # the caption is collapsed with the top margin of the table. 

This caption should be fixed so that it doesn't say the margins
collapse.

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/