SkPDF: remove suppression

Review URL: https://codereview.chromium.org/1379183005
diff --git a/tools/tsan.supp b/tools/tsan.supp
index 0401197..4333ec2 100644
--- a/tools/tsan.supp
+++ b/tools/tsan.supp
@@ -15,4 +15,3 @@
 # Not threadsafe, should be fixed.
 race:RefFCI
 race:SkString
-race:SkPDF