As mentioned in today's monthly update video, the Open With menu
doesn't show Pixel Paint for most image file types.
This commit brings it in sync with Image Viewer,
since everything seems to open correctly anyway :)
With everything now using GUI::FileIconProvider and therefore loading
icons embedded in the executable files, this information is now longer
being used.
We might have to think about this again if we want to allow .af files
with custom commands (e.g. shell scripts). Maybe those could get away
with just an "Icon" entry under "[App]", but currently there's only
"Executable" anyway.
