Disable unpremul f16 image tests

Testing premul f16 is enough test coverage, and we aren't doing
this correctly right now anyways (the drawing code assumes a
premul bitmap, we would need to premultiply after the unpremul
decode).

BUG=skia:

Change-Id: I798f56db67faadd0348974453a05cd726b9a509c
Reviewed-on: https://skia-review.googlesource.com/8020
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
1 file changed