[test] Remove TEARDOWN macro, use managed pointers instead

Clean-up to remove explicit resource deallocation by using unique_ptr
instead.

R=mstarzinger@chromium.org

Bug: v8:8562
Change-Id: I603cf1b9e2cfe33bc7e6bd84cdd228cf10ff20ba
Reviewed-on: https://chromium-review.googlesource.com/c/1415492
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58886}