Tidy up some README.chromium files in Angle. Backfills the Update Mechanism field for dependencies and cleans up some of the other fields which are out of date. Bug: chromium:379934539 Change-Id: I9a952e905ce00c379c4d593dd67b7e0fc6f1794e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6981101 Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>