Remove the suppression for issue 181502 (races on std::string internals)

TSan is using instrumented libc++ now, so these false positives aren't reported anymore.

BUG=181502
TBR=earthdok@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/257773005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266301 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/tsan_v2/suppressions.txt

@@ -47,10 +47,6 @@ race:media::ReleaseData
 # http://crbug.com/158922
 race:third_party/libvpx/source/libvpx/vp8/encoder/*
 
-# See http://crbug.com/181502
-race:_M_rep
-race:_M_is_leaked
-
 # http://crbug.com/189177
 race:thread_manager
 race:v8::Locker::Initialize