Remove a bunch of fixed position dead code.

sky/engine/public/platform/WebLayer.h

Index: sky/engine/public/platform/WebLayer.h
diff --git a/sky/engine/public/platform/WebLayer.h b/sky/engine/public/platform/WebLayer.h
index 3950cc1d5342dc5e9e1c4c22aab629d646c211e6..2426cc56f9dbf811b5aafe8bead6757d02962be7 100644
--- a/sky/engine/public/platform/WebLayer.h
+++ b/sky/engine/public/platform/WebLayer.h
@@ -189,11 +189,6 @@ public:
     virtual void setIsContainerForFixedPositionLayers(bool) = 0;
     virtual bool isContainerForFixedPositionLayers() const = 0;
 
-    // This function sets layer position constraint. The constraint will be used
-    // to adjust layer position during threaded scrolling.
-    virtual void setPositionConstraint(const WebLayerPositionConstraint&) = 0;
-    virtual WebLayerPositionConstraint positionConstraint() const = 0;
-
     // The scroll client is notified when the scroll position of the WebLayer
     // changes. Only a single scroll client can be set for a WebLayer at a time.
     // The WebLayer does not take ownership of the scroll client, and it is the