Do not build the ktx encoder for android framework

Move SkKTXImageEncoder.cpp into an optional block, and disable that
block for the android framework. Use a new define to determine whether
to define the entry point, rather than using
SK_BUILD_FOR_ANDROID_FRAMEWORK.

Change-Id: I41103459135af744cf5715f27783c63dc37a7ad1
Reviewed-on: https://skia-review.googlesource.com/5982
Commit-Queue: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
3 files changed