Remove DesktopCapturer::Callback::OnCaptureCompleted()

The method was deprecated and shouldn't be used anywhere now.

BUG=webrtc:5950

Review-Url: https://codereview.webrtc.org/2080573004
Cr-Original-Commit-Position: refs/heads/master@{#13248}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6ef36e708f47eb3a42c42091ab975a2186700604
1 file changed