api: remove getViewportWidget()

The returned widget isn't actually the viewport widget, but is a layer within the viewport, and only needs to be used within the overlay renderer to position the snapcorners

runelite-api/src/main/java/net/runelite/api/Client.java

@@ -879,16 +879,6 @@ public interface Client extends GameEngine
 	 */
 	IterableHashTable<MessageNode> getMessages();
 
-	/**
-	 * Gets the viewport widget.
-	 * <p>
-	 * The viewport is the area of the game above the chatbox
-	 * and to the left of the mini-map.
-	 *
-	 * @return the viewport widget
-	 */
-	Widget getViewportWidget();
-
 	/**
 	 * Gets the object composition corresponding to an objects ID.
 	 *