Retire Valgrind suppression for WebVTTParser

This was originally suspected fixed in 2012.

The suppression hasn't fired since Jan 2013.

BUG=138058
R=annacc@chromium.org

Review-Url: https://codereview.chromium.org/1993193002
Cr-Original-Commit-Position: refs/heads/master@{#415895}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5a8a883c7d3952e1aa8d743edaca2e9c9bda74af
1 file changed