Remove unused variable in value-serializer.cc

This CL fixes the clang ToT bots.

R=jarin@chromium.org,neis@chromium.org

Change-Id: If903c59cb2ed70fcb3115310df71ba1e924ef824
Reviewed-on: https://chromium-review.googlesource.com/729244
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48772}

src/value-serializer.cc

@@ -1582,7 +1582,6 @@ MaybeHandle<JSSet> ValueDeserializer::ReadJSSet() {
 MaybeHandle<JSArrayBuffer> ValueDeserializer::ReadJSArrayBuffer() {
   uint32_t id = next_id_++;
   uint32_t byte_length;
-  Vector<const uint8_t> bytes;
   if (!ReadVarint<uint32_t>().To(&byte_length) ||
       byte_length > static_cast<size_t>(end_ - position_)) {
     return MaybeHandle<JSArrayBuffer>();