This also removes the IS_GLOBAL macro from macros.py, which did
not work correctly for Remote objects/contexts.

Bug: v8:6413
Change-Id: I90690bdd0d8e8fed581bc4c9f5c60168d785f096
Reviewed-on: https://chromium-review.googlesource.com/633872Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47585}