[iwyu] Don't include "unicode.h" from "objects.h".

R=marja@chromium.org
BUG=v8:7490

Change-Id: Ib95662764db5659bd312327021cf5f44493c1cb3
Reviewed-on: https://chromium-review.googlesource.com/1057147Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53149}

src/objects.h

@@ -18,8 +18,6 @@
 #include "src/flags.h"
 #include "src/messages.h"
 #include "src/property-details.h"
-#include "src/unicode-decoder.h"
-#include "src/unicode.h"
 
 #if V8_TARGET_ARCH_ARM
 #include "src/arm/constants-arm.h"  // NOLINT

src/objects/string.h

@@ -7,6 +7,7 @@
 
 #include "src/base/bits.h"
 #include "src/objects/name.h"
+#include "src/unicode-decoder.h"
 
 // Has to be the last include (doesn't have include guards):
 #include "src/objects/object-macros.h"