* sem_prag.adb (Duplication_Error): Remove the special handling
of 'Class or _Class in the context of pre/postconditions.
(Process_Class_Wide_Condition): Remove the special handling of
'Class or _Class in the context of pre/postconditions.
* sem_util.adb (Original_Aspect_Pragma_Name): Names Pre_Class
and Post_Class no longer need to be converted to _Pre and _Post.
* sem_util.ads (Original_Aspect_Pragma_Name): Update the comment
on usage.