Remove support for png2ico

Png2Ico provides lower quality icons compared to icoutils as png2ico predates the current icon standard. Still lloking for png2ico prints

• Png2Ico, Executable that converts a collection of PNG files into a Windows icon file, <https://www.winterdrache.de/freeware/png2ico/ or https://commits.kde.org/kdewin>

which confuses new users.