Reenable 16-bit png brd decode tests

I accidentally turned these off in:
https://skia-review.googlesource.com/c/6023/

Even though the decode color type does not match the canvas,
we still want to run the test.

BUG=skia:

Change-Id: Ia96069a44e20d62a58d37a98bac81cfab5470fc0
Reviewed-on: https://skia-review.googlesource.com/6088
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed