This reverts commit 24aca870.

The API makes these values appear to be per-isolate, when in fact
they are per-context. Installing the results of these on Template
objects instantiated in multiple contexts can result in security
violations and contexts being retained indefinitely.

An alternative mechanism for using these in a sensible way is
provided by https://crrev.com/1409593002

BUG=
LOG=N
R=jochen@chromium.org, adamk@chromium.org

Review URL: https://codereview.chromium.org/1415663002

Cr-Commit-Position: refs/heads/master@{#31417}