Revert of Discard atlas after every MultiPictureDraw::draw (patchset #4 id:60001 of https://codereview.chromium.org/678403002/)

Reason for revert:
Breaking bots

Original issue's description:
> Discard atlas after every MultiPictureDraw::draw
>
> This is intended to prevent ghosting on tiled architectures.
>
> This CL also defers creation of the atlas (and its texture) until it is actually needed.
>
> Committed: https://skia.googlesource.com/skia/+/6d5b5455743414ddb11d2b8c1fe9d7959f2b853d

TBR=bsalomon@google.com
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/687233002
diff --git a/src/gpu/GrLayerCache.h b/src/gpu/GrLayerCache.h
index 632cd00..c772332 100644
--- a/src/gpu/GrLayerCache.h
+++ b/src/gpu/GrLayerCache.h
@@ -18,9 +18,6 @@
 
 class SkPicture;
 
-// Set to 0 to disable caching of hoisted layers
-#define GR_CACHE_HOISTED_LAYERS 0
-
 // The layer cache listens for these messages to purge picture-related resources.
 struct GrPictureDeletedMessage {
     uint32_t pictureID;
@@ -252,10 +249,6 @@
         return width <= kPlotWidth && height <= kPlotHeight;
     }
 
-#if !GR_CACHE_HOISTED_LAYERS
-    void purgeAll();
-#endif
-
 private:
     static const int kAtlasTextureWidth = 1024;
     static const int kAtlasTextureHeight = 1024;
@@ -298,6 +291,8 @@
                                const SkIRect& bounds, const SkMatrix& ctm, 
                                const SkPaint* paint);
 
+    void purgeAll();
+
     // Remove all the layers (and unlock any resources) associated with 'pictureID'
     void purge(uint32_t pictureID);