Under certain conditions, program icons loaded on Windows via GDI+ have
empty mask data, even though the original icon has proper mask data. As
a result, these icons are printed with a black instead of a transparent
background. This only happens when retrieving icons via the program's
file extension but works properly when using the (also available) full
icon path.

With this change, the shortcut functionality retrieving an icon from a
program's file extension is removed, so that the icon is always
retrieved from its full path. This fixes the issue with missing mask
data and reduces code.

Fixes https://github.com/eclipse-platform/eclipse.platform.swt/issues/715