Retire call capture listeners flag

Retire the stable flag
CallCaptureListenersAtCapturePhaseAtShadowHosts

The flag has been stable since
https://chromium-review.googlesource.com/1229741

BUG=883650

Change-Id: Ib7468e3dde14b28e32587f9c9a100debcfee88ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1616713
Reviewed-by: Hayato Ito <hayato@chromium.org>
Reviewed-by: Fernando Serboncini <fserb@chromium.org>
Commit-Queue: Fernando Serboncini <fserb@chromium.org>
Auto-Submit: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661764}
4 files changed