third_party/ktx: put WriteBitmapToKTX back

BUG=skia:

Change-Id: I876e802db370a7812cd53e42cb4927702e6c1fb6
Reviewed-on: https://skia-review.googlesource.com/5418
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed