d: Remove handling of deleting GC allocated classes.

d: Remove handling of deleting GC allocated classes.

Now that the `delete' keyword has been removed from the front-end, only
compiler-generated uses of DeleteExp reach the code generator via the
auto-destruction of `scope class' variables.

The run-time library helpers that previously were used to delete GC
class objects can now be removed from the compiler.

gcc/d/ChangeLog:

	* expr.cc (ExprVisitor::visit (DeleteExp *)): Remove handling of
	deleting GC allocated classes.
	* runtime.def (DELCLASS): Remove.
	(DELINTERFACE): Remove.