Revert "Reduce dirty image pages by improving binning"

This reverts commit 794bff5f622c79fd7bd9899e700cf052a375c675.

(cherry picked from commit 8ace610a222892f7b700e4f95e50fa6315ab85c0)

Change-Id: Id53d64a04aa8766a2cb283a2f7b8354590213b13
diff --git a/imgdiag/imgdiag.cc b/imgdiag/imgdiag.cc
index cbd0c40..c2a812e 100644
--- a/imgdiag/imgdiag.cc
+++ b/imgdiag/imgdiag.cc
@@ -416,8 +416,7 @@
     // Look up local classes by their descriptor
     std::map<std::string, mirror::Class*> local_class_map;
 
-    // Use set to have sorted output.
-    std::set<mirror::Object*> dirty_objects;
+    std::unordered_set<mirror::Object*> dirty_objects;
 
     size_t dirty_object_bytes = 0;
     const uint8_t* begin_image_ptr = image_begin_unaligned;