Also remove a few bits of related dead code in Parser.

Bug: v8:6092
Change-Id: I310936341fe3e6193e36983723985a190d5d278b
Reviewed-on: https://chromium-review.googlesource.com/621958
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47518}