Update README

Author: mbostock

README.md

@@ -464,9 +464,3 @@ An array of ImportSpecifier nodes, if the import declaration has a `with` clause
 <a href="specifier_view" name="specifier_view">#</a> <i>specifier</i>.<b>view</b>
 
 A boolean indicating whether the import specifies a view.
-
-### Program
-
-<a href="#program_cells" name="program_cells">#</a> <i>program</i>.<b>cells</b>
-
-An array of [cells](#cell).