Rip out Settings::fixedPositionCreatesStackingContext

LayoutTests/compositing/geometry/limit-layer-bounds-fixed-expected.txt

 (GraphicsLayer
   (bounds 785.00 5013.00)
   (children 1
     (GraphicsLayer
       (bounds 785.00 5013.00)
       (contentsOpaque 1)
       (drawsContent 1)
       (children 2
         (GraphicsLayer
           (position 100.00 3100.00)
           (bounds 100.00 100.00)
           (contentsOpaque 1)
           (drawsContent 1)
           (backgroundColor #FF0000)
         )
         (GraphicsLayer
-          (position 100.00 3100.00)
-          (bounds 200.00 100.00)
-          (contentsOpaque 1)
+          (position 0.00 3000.00)
+          (bounds 300.00 200.00)
           (drawsContent 1)
           (backgroundColor #008000)
         )
       )
     )
   )
 )