revert Mark interface change

Author: mbostock

src/mark.d.ts

@@ -453,9 +453,6 @@ export interface MarkOptions {
 
 /** The abstract base class for Mark implementations. */
 export class Mark {
-  /** The mark’s data. */
-  data?: Data;
-
   /**
    * Renders a new plot, prepending this mark as the first element of **marks**
    * of the specified *options*, and returns the corresponding SVG element, or