Remove the old tcmalloc code

Nobody uses it anymore.
Depends on http://crrev.com/c/1754158.

BUG=989976,b:131626644

Change-Id: I04bd32cf285b46b79c22f997ef6dc972ec55e8f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1754159
Reviewed-by: Gabriel Marin <gmx@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#687304}