Remove a suppression for bug 18488 since it should be fixed already.

Review URL: http://codereview.chromium.org/215021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@26593 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/tsan/suppressions.txt

@@ -8,14 +8,6 @@
   fun:*URLRequestJobTracker*
 }
 
-{
-  bug_18488
-  ThreadSanitizer:Race
-  ...
-  fun:*RefCountedBase*
-  fun:*HostResolver*
-}
-
 {
   bug_21259
   ThreadSanitizer:Race