Remove scanlineOrder switch statements that always do the same thing

I think these date back to GIF codec having a third value of this enum
that meant "interlaced" ?

Change-Id: Iaff11a55ad3cff44da2307149991a22447dfe746
Reviewed-on: https://skia-review.googlesource.com/119146
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed