Delete rtc_event_log/ringbuffer.h

This code is unused since https://codereview.webrtc.org/2875823003/ and the current implementation is too specific to the event log to be useful elsewhere. I think we should get add a reusable cyclic buffer though and I made a rough draft of what it might look like: https://codereview.webrtc.org/2691073002/

BUG=webrtc:7732

Review-Url: https://codereview.webrtc.org/2923163006
Cr-Original-Commit-Position: refs/heads/master@{#18465}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: f53c4cd8674f3719799aaf0c926d8d23985b89b6
4 files changed