Remove all KTX support

It is untested and unused.

Change-Id: I010ff4ad942738f362d42a99af4edbbb1cb0cd71
Reviewed-on: https://skia-review.googlesource.com/6142
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Robert Phillips <robertphillips@google.com>
8 files changed