Remove stale sctp_timer_start suppression

I believe this was fixed upstream in
ec03a56a31

Confirmed race no longer reproduces locally, and if I comment out the locks
added above, it does.

Bug: 347538
Change-Id: I313f5ed4aafbf012ffa4543580f3b3a5541c2c2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1657299
Auto-Submit: David Benjamin <davidben@chromium.org>
Commit-Queue: Tommi <tommi@chromium.org>
Reviewed-by: Tommi <tommi@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#669608}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a4c22d7cb98a446c1e72a9b5c1ea5c32845a5ea9

sanitizers/tsan_suppressions.cc

@@ -110,9 +110,6 @@ char kTSanDefaultSuppressions[] =
     // http://crbug.com/328868
     "race:PR_Lock\n"
 
-    // http://crbug.com/347538
-    "race:sctp_timer_start\n"
-
     // http://crbug.com/348982
     "race:cricket::P2PTransportChannel::OnConnectionDestroyed\n"
     "race:cricket::P2PTransportChannel::AddConnection\n"