It was removed so that Parser::DeserializeScopeChain does not have
 to get it from ParseInfo.
Only a small step in direction of removing isolate from ParseInfo.

BUG=v8:6093

Change-Id: Iaaf92dc6eb5ec9c4efc05ac73666fbc66e0ed8c1
Reviewed-on: https://chromium-review.googlesource.com/457999
Commit-Queue: Wiktor Garbacz <wiktorg@google.com>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44057}