Simpler way to deal with the FBO multi-cache.

This change removes the need for the SortedList and instead just
add a generated id to each FBO stored in the cache. This is an
artificial way to store several FBOs with the same dimensions.

Change-Id: I9638364e9bdc0f2391261937a0c86096f20505bf
diff --git a/libs/hwui/LayerCache.h b/libs/hwui/LayerCache.h
index 2d339fa..519552d 100644
--- a/libs/hwui/LayerCache.h
+++ b/libs/hwui/LayerCache.h
@@ -66,7 +66,8 @@
 private:
     void deleteLayer(Layer* layer);
 
-    GenerationMultiCache<LayerSize, Layer*> mCache;
+    GenerationCache<LayerSize, Layer*> mCache;
+    uint32_t mIdGenerator;
 
     uint32_t mSize;
     uint32_t mMaxSize;