remove third_party/etc1

Nothing seems to reference it.

Change-Id: Ib009a7dc33d31439b11588758015a07485f56eaa
Reviewed-on: https://skia-review.googlesource.com/99861
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
6 files changed