remove Skia kDifference workaround

I thought it was a driver problem, but now I'm actually not sure,
as I cannot reproduce it anymore and I don't know if it was a driver
update or Skia update. Either way, this works now.

Also switch to kExclusion, because the end result is the same,
but this formula is simpler (to understand primarily, the performance
is going to be probably the same).

Change-Id: I6ced098ca4a3361cf98d3f9b32968c128eb9f299
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/126050
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

0 files changed, 0 insertions, 0 deletions