The generation of unwind info to enable stack walking on Windows/x64
(https://chromium-review.googlesource.com/c/v8/v8/+/1469329) was implemented
behind a temporary flag, in order to coordinate these changes with the
corresponding changes in Chromium.

The required changes to Chromium
(https://chromium-review.googlesource.com/c/chromium/src/+/1474703) have also
been merged, so we can now remove the flag and enable the generation of stack
unwinding info by default on Windows/x64.

Bug: v8:3598
Change-Id: I88814aaeabecc007f5262227aa0681a1d16156d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1573138Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Paolo Severini <paolosev@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#61020}