Bug 1450134. Remove ToRelativeLayoutPoint(). r=kats

It's completely unused.

--HG--
extra : rebase_source : 235f41e637502a7d44292faea4b003e60c460dcb

gfx/layers/wr/StackingContextHelper.h

@@ -60,12 +60,6 @@ public:
   // We also round the rectangle to ints after transforming since the output
   // is the final destination rect.
   wr::LayoutRect ToRelativeLayoutRect(const LayoutDeviceRect& aRect) const;
-  // Same but for points
-  wr::LayoutPoint ToRelativeLayoutPoint(const LayoutDevicePoint& aPoint) const
-  {
-    return wr::ToLayoutPoint(aPoint);
-  }
-
 
   // Export the inherited scale
   gfx::Size GetInheritedScale() const { return mScale; }