Remove SetModal interface.

widget/public/nsIWidget.h

@@ -253,13 +253,6 @@ class nsIWidget : public nsISupports {
      */
     NS_IMETHOD Show(PRBool aState) = 0;
 
-    /**
-     * Make the window modal 
-     *
-     *
-     */
-    NS_IMETHOD SetModal(void) = 0;
-
     /**
      * Returns whether the window is visible
      *