This flag was originally added as a staging mechanism to let us land and test
guard regions without the full trap handler feature landing. Additionally, we
thought we might enable guard regions without trap handlers on some systems.

Trap handlers are now supported, and there's not a real compelling reason for
why we need guard regions without trap handlers. Keeping the separate flag leads
to confusion, since some code treats guard regions and trap handlers the same,
while other code treats them as independent.

Removing this flag and its associated special cases makes everything more
uniform and predictable.

R=gdeepti@chromium.org

Change-Id: Icebab91d1f1e0c55e7a35c75b880085d37fa14ae
Reviewed-on: https://chromium-review.googlesource.com/706570Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48411}