remove unused parameter in onNewimageSnapshot

BUG=skia:

Change-Id: I59b4cbace841489698fb22828c35b82a738d06b3
Reviewed-on: https://skia-review.googlesource.com/6494
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
4 files changed