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/entrypoints/entrypoint_utils-inl.h b/runtime/entrypoints/entrypoint_utils-inl.h
index 482ad47..542e1a9 100644
--- a/runtime/entrypoints/entrypoint_utils-inl.h
+++ b/runtime/entrypoints/entrypoint_utils-inl.h
@@ -25,12 +25,12 @@
 #include "indirect_reference_table.h"
 #include "invoke_type.h"
 #include "jni_internal.h"
+#include "method_helper.h"
 #include "mirror/art_method.h"
 #include "mirror/array.h"
 #include "mirror/class-inl.h"
 #include "mirror/object-inl.h"
 #include "mirror/throwable.h"
-#include "object_utils.h"
 #include "handle_scope-inl.h"
 #include "thread.h"