Remove unused native method

depends on external/webkit change: https://android-git.corp.google.com/g/#/c/190468/

bug:6486310
Change-Id: Id1c1eabf27135c73e45a489ab4c7cfa26e0c9def

Author: ChrisCraik

core/java/android/webkit/WebViewClassic.java

@@ -8648,7 +8648,6 @@ private native int      nativeCreateDrawGLFunction(int nativeInstance, Rect invS
     private native void     nativeUpdateDrawGLFunction(int nativeInstance, Rect invScreenRect,
             Rect screenRect, RectF visibleContentRect, float scale);
     private native String   nativeGetSelection();
-    private native Rect     nativeLayerBounds(int layer);
     private native void     nativeSetHeightCanMeasure(boolean measure);
     private native boolean  nativeSetBaseLayer(int nativeInstance,
             int layer, boolean showVisualIndicator, boolean isPictureAfterFirstLayout);