Cleanup: Remove 4 matured deprecated symbols with zero external usage

This CL removes the first batch of deprecated symbols from the WebRTC API and internal headers. All removed symbols have zero confirmed    external usage in google3 and have been deprecated for at least 3 months.

This iteration successfully retires 5 matured symbols with verified zero usage across WebRTC, google3, Chromium, and WebKit:
   * Candidate::ToSanitizedCopy (2-arg variant)
   * VideoFrame::Builder::set_capture_time_identifier
   * RtcEventLogFactory (1-arg constructor)
   * VideoQualityAnalyzerInterface::OnFrameDropped (2-arg variant)

Bug: webrtc:9725, webrtc:467444018
Change-Id: Ia4399107863db9f5866590a89ef290a94884b79e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/466383
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47558}