[RFA] Remove obsolete / deprecated cruft

[Nicola Pero]

> >Note that
> >#import hasn't changed (I'm inclined to un-deprecate it to be honest,
> >in view of its pervasiveness in Obj-C land.)
> >
> But that would take away one of the selling points for Apple GCC
> over FSF GCC! :-)
> 
> Seriously though, I'm inclined to leave it deprecated in FSF GCC,
> just to act as a gentle encouragement to use include guards.

Yes - I agree.

It probably doesn't make much of a difference either way.

At least for GNUstep (which is at the moment the biggest user of FSF GCC
ObjC) it doesn't make much of a difference, since all the gnustep core
libraries are protected against multiple inclusions in all cases, and the
gnustep make system automatically slips in the -Wno-import flag whenever
GCC is used, so none of our users actually ever sees that warning.  Many
of them don't even know it exists.

Personally, I occasionally do use the warning to check that all headers in
a package (when many other people contributed to it) have been properly
protected against multiple inclusions via include guards, and no #import
has been used, but I suspect very few other people do this.

But I think if the warning has a technical reason to exist, it should
stay.

Btw, how good is the support for #import under Microsoft Windows ?