Remove object_utils.h.

Break into object_lock, field_helper and method_helper.
Clean up header files following this.
Also tidy some of the Handle code in response to compiler errors when resolving
the changes in this CL.

Change-Id: I73e63015a0f02a754d0866bfaf58208aebcaa295
diff --git a/runtime/proxy_test.cc b/runtime/proxy_test.cc
index 57eb3f7..bd6656d 100644
--- a/runtime/proxy_test.cc
+++ b/runtime/proxy_test.cc
@@ -18,6 +18,7 @@
 #include <vector>
 
 #include "common_compiler_test.h"
+#include "field_helper.h"
 #include "mirror/art_field-inl.h"
 #include "scoped_thread_state_change.h"