Remove SkKTXImageEncoder

It escaped the chopping block when we deleted the decoder, but it is
currently untested and unused as far as we know. In addition to
removing effectively unsupported code, this simplifies build file
changes (i.e. don't build it on Android framework, but build it
elsewhere) as we narrow our build systems down to one.

Change-Id: I3b960fdcc369fb947be282933ddba48e407ab3ad
Reviewed-on: https://skia-review.googlesource.com/6031
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Leon Scroggins <scroggo@google.com>
5 files changed