libpthread: Remove a comment which I missed in my earlier change
libpthread: Remove a comment which I missed in my earlier change

The comment refers to a thread ID field that I removed.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=2788
TEST=none

Review URL: https://chromiumcodereview.appspot.com/10386227

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@8662 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client