Revert "Use new tcmalloc on Linux builds by default."

This reverts commit f7c11345.

Reason for revert: suspected of causing sizes failure on linux-rel build bot.
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/linux-rel/9414

Original change's description:
> Use new tcmalloc on Linux builds by default.
>
> This changes the default version of tcmalloc used by Chrome on Linux
> from a modified tcmalloc 2.0 to a modified tcmalloc 2.7.
>
> See discussion at http://shortn/_db7vovHkbm for benchmarks and analysis.
>
> BUG=724399
>
> Change-Id: I75b89fcb0e22c2ca627634a6581c937608f4ce6f
> Reviewed-on: https://chromium-review.googlesource.com/c/1278949
> Commit-Queue: Will Harris <wfh@chromium.org>
> Reviewed-by: Scott Graham <scottmg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#605104}

TBR=scottmg@chromium.org,wfh@chromium.org,gmx@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 724399
Change-Id: I87bb7d8c826207d6cad159efc4c26e8c88707135
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/1316950
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605228}

build/config/allocator.gni

@@ -34,7 +34,7 @@ declare_args() {
   use_partition_alloc = !is_ios
 
   # Use the new tcmalloc. It's relevant only when use_allocator == "tcmalloc".
-  use_new_tcmalloc = is_linux && !is_chromeos
+  use_new_tcmalloc = false
 }
 
 if (is_nacl) {