Remove FusedSilica?

[Fred Kiefer]

While going through the internal GNUstep headers I noticed that we still
have the place holders for CoreGraphics in there that Adam added a few
years ago. Now with an ever more complete implementation of CoreGraphics
in opal these seem obsolete to me. Should we just remove them?
The only drawback I can think of is an application that did not directly
request CoreGraphics by importing a header, but relied on AppKit
providing it. But such an application was wrong in the first place and
it is also highly unlikely that any application could work with the the
minimal subset of CoreGraphics that was implemented in FusedSilica. All
of these operations have direct mappings in AppKit and the application
should be changed to use these.

Another limitation is that Opal will only work with the cairo backend
and I doubt that will will currently work with a combination of AppKit
and CoreGraphics calls, but hopefully this gets resolved soon.

We don't have to remove it now. This is something I would like to
resolve before the 1.0 release of gui.

Fred