Revert "Enable proprietary_codecs=true by default."

This reverts commit 7f446eb0ecff4014853501cd6d50fcf8ff6fa98b.

Reason for revert: reverting for now, now that we've established that it seems to work.

Original change's description:
> Enable proprietary_codecs=true by default.
>
> We want most of our test coverage to be done against builds with
> the proprietary codecs included, so this changes the default to
> do so. However, it is important that we *not* publicize or distribute
> any builds that includes these codecs (since they likely won't have
> the correct licensing), and so we explicitly turn the flag off on
> the builders that do publish builds.
>
> This change includes a roll of the FFmpeg repo from 423f74fa..c94da9e8
> in order to pick up that change, which changes ffmpeg to pick up
> `ffmpeg_branding`'s default value directly from `proprietary_codecs`,
> making the actual ffmpeg_branding GN arg kinda pointless (the branding
> is now driven by proprietary_codecs and is_chromeos).
>
> R=​[email protected], [email protected], [email protected], [email protected]
>
> Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
> Change-Id: Id0b6cccbd235875c9386a527cb39c8f17d2dab03
> Reviewed-on: https://chromium-review.googlesource.com/832383
> Reviewed-by: Chrome Cunningham <[email protected]>
> Reviewed-by: Kenneth Russell <[email protected]>
> Commit-Queue: Dirk Pranke <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#525172}

[email protected],[email protected],[email protected],[email protected],[email protected]
BUG=795935

Change-Id: I30b9d447facc94f3eaaa55c7252e3f050720619f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Reviewed-on: https://chromium-review.googlesource.com/836414
Commit-Queue: Dirk Pranke <[email protected]>
Reviewed-by: Dirk Pranke <[email protected]>
Cr-Commit-Position: refs/heads/master@{#525364}
4 files changed