Log Message:
graphics/oxipng: update to 8.0.0

 - [Breaking] Revamp alpha optimization
 - [Bugfix] Fix grayscale depth reduction with tRNS pixel
 - [Bugfix] Fix fast mode with zopfli
 - [Improvement] Tweaks to interlacing and format display
 - [Improvement] Ability to reduce alpha channel to tRNS pixel
 - [Improvement] Performance improvements to colorspace reduction
 - [Misc] Disable image validation in release mode, as it is deemed no longer
   necessary