Revert "Make compiler/optimizing/ symbols hidden."

This reverts commit e2727154f25e0db9a5bb92af494d8e47b181dfcf.

Reason for revert: Breaks ASAN tests (ODR violation).
Bug: 142365358

Change-Id: I38103d74a1297256c81d90872b6902ff1e9ef7a4
diff --git a/compiler/optimizing/scheduler.h b/compiler/optimizing/scheduler.h
index 9bf0aa7..a97eda7 100644
--- a/compiler/optimizing/scheduler.h
+++ b/compiler/optimizing/scheduler.h
@@ -19,7 +19,6 @@
 
 #include <fstream>
 
-#include "base/macros.h"
 #include "base/scoped_arena_allocator.h"
 #include "base/scoped_arena_containers.h"
 #include "base/stl_util.h"
@@ -29,7 +28,7 @@
 #include "nodes.h"
 #include "optimization.h"
 
-namespace art HIDDEN {
+namespace art {
 
 // General description of instruction scheduling.
 //