Rollup merge of #22916 - rprichard:fmt-num-cleanup, r=alexcrichton

  * Make num::UpperHex private.  I was unable to determine why this struct
   is public.  The num module itself is not public, and the UpperHex struct
   is not referenced anywhere in the core::fmt module.  (Only the UpperHex
   trait is reference.)  num::LowerHex is not public.

 * Remove the suffix parameters from the macros that generate integral
   display traits.

   The code to print the Debug::fmt suffixes was removed when Show was
   renamed to Debug.  It was an intentional change.  From RFC 0565:

    * Focus on the *runtime* aspects of a type; repeating information such
      as suffixes for integer literals is not generally useful since that
      data is readily available from the type definition.

 * Because Show was renamed to Debug, rename show! to debug!.