Revert of Depend on ETC1 via DEPS instead of a direct third_party checkin. (patchset...

Revert of Depend on ETC1 via DEPS instead of a direct third_party checkin. (patchset #1 id:1 of https://codereview.chromium.org/1296253003/ )

Reason for revert:
This will make the google3 roll awkward.  Reverting.

Original issue's description:
> Depend on ETC1 via DEPS instead of a direct third_party checkin.
>
> Yes, this does mean we'll check out ~40M of code for 2 files...
>
> I think these trybots are moot... they gclient sync before patching.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/ca01d179347b5e848ded97c8228b79ffc6b5e7bf

TBR=robertphillips@google.com,djsollen@google.com,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1290913008