remove dead code for legacy image encode api

Bug: skia:
Change-Id: Ia90d776946281473c56cd93006df1b523475696a
Reviewed-on: https://skia-review.googlesource.com/23022
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Reed <reed@google.com>
3 files changed