[gyp] delete last vestiges of gyp.

R=franzih@chromium.org

Bug: v8:7335
Change-Id: Icd4624b119f573640bd34b19db1f6c1b7e035f8d
Reviewed-on: https://chromium-review.googlesource.com/910930Reviewed-by: Franziska Hinkelmann <franzih@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51199}