surfaceflinger: remove DisplayDevice::swapRegion

With SWAP_RECTANGLE and PARTIAL_UPDATES removed, it becomes clear
that swapRegion is not needed.  It also becomes clear that
DisplayDevice::flip and SurfaceFlinger::doComposeSurfaces do not
need the dirty region.

Test: SurfaceFlinger_test
Change-Id: Id9cd2b43812d3c7dcfa36f605d0f8a647264f228
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index e454ef7..7aa16de 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -201,7 +201,7 @@
     return mPageFlipCount;
 }
 
-void DisplayDevice::flip(const Region& /*dirty*/) const
+void DisplayDevice::flip() const
 {
     mFlinger->getRenderEngine().checkErrors();
     mPageFlipCount++;