Revert "about_flags.cc entry for WebRTC-H264WithOpenH264FFmpeg"

Reason: This breaks WebRTC standalone from rolling chromium_revision
in the DEPS file. See https://codereview.webrtc.org/1765393002/ for examples.
The problem is that the Chromium build/common.gypi gets a hardcoded
dependency into ../third_party/webrtc/build/common.gypi, which doesn't
resolve when a standalone WebRTC checkout tries to process Chromium's
build/common.gypi.

For reland: Please move the rtc_use_h264 variable into Chromium's GYP chain
if it needs to be accessed from this context.

This reverts commit 8018fbdf7bd32858d8926772e54c9ee20227d403.
> about_flags.cc entry for WebRTC-H264WithOpenH264FFmpeg
> (base::Feature kWebRtcH264WithOpenH264FFmpeg).

> This is a feature that enables a H.264 encoder/decoder in
> WebRTC. The feature is off by default.

> BUG=chromium:500605, chromium:468365
> Committed: https://crrev.com/8018fbdf7bd32858d8926772e54c9ee20227d403
> Cr-Commit-Position: refs/heads/master@{#379284}

TBR=hbos@chromium.org, jochen@chromium.org, flackr@chromium.org, asvitkine@chromium.org, rkaplow@chromium.org,
BUG=chromium:500605, chromium:468365

Review URL: https://codereview.chromium.org/1770683002

Cr-Commit-Position: refs/heads/master@{#379488}
6 files changed