Node.js doesn't build because v8_extra_library_files is
used but not defined in v8.gyp.

We can probably clean up the build file and properly
delete v8_extra_library_files, just want to get the integration
build green again.

TBR=adamk@chromium.org

BUG=

Review-Url: https://codereview.chromium.org/2720483002
Cr-Commit-Position: refs/heads/master@{#43429}