This removes:
- V8::AddGCPrologueCallback
- V8::RemoveGCPrologueCallback
- V8::AddGCEpilogueCallback
- V8::RemoveGCEpilogueCallback

The emebedder should use the Isolate versions of these functions.

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I7974bc7478e542f29483cf939b33dbb872a3b41d
Reviewed-on: https://chromium-review.googlesource.com/788053Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49617}