remove 'deprecated' region from SkDraw

Most call-sites that used it just took its bounds, so it was trivial to convert them
to get the bounds of the RasterClip. Two clients wanted the actual region:
1. layeriter for android
2. pdf

Android already only has BW clips, so should be safe.
PDF now overrides its clip methods to ensure that all clips are BW.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1925693002

Review URL: https://codereview.chromium.org/1925693002
diff --git a/tests/CanvasTest.cpp b/tests/CanvasTest.cpp
index f22b7d0..1f217e2 100644
--- a/tests/CanvasTest.cpp
+++ b/tests/CanvasTest.cpp
@@ -55,6 +55,7 @@
 #include "SkPicture.h"
 #include "SkPictureRecord.h"
 #include "SkPictureRecorder.h"
+#include "SkRasterClip.h"
 #include "SkRect.h"
 #include "SkRegion.h"
 #include "SkShader.h"
@@ -507,7 +508,7 @@
                 return false;    
             }
             if (layerIter1.clip() != layerIter2.clip()) {
-                return false;    
+                return false;
             }
             if (layerIter1.paint() != layerIter2.paint()) {
                 return false;