Also a few bits of related dead code in Parser.

Bug: v8:6092
Change-Id: Ie30aa1bd769b78fec2563fc6ba82ef0bcd7668bb
Reviewed-on: https://chromium-review.googlesource.com/639311Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47688}