remove filelock which is now unused

R=pthatcher@webrtc.org

Committed: https://crrev.com/5ece00f7fa15407314aa27ae5c262a86f004468a
Cr-Commit-Position: refs/heads/master@{#9222}

Review URL: https://webrtc-codereview.appspot.com/51859004

Cr-Commit-Position: refs/heads/master@{#9225}
1 file changed