Don't use <ctype.h> macros.

They're locale-dependent (although those *particular* ones might not
be).

Remove no-longer necessary (or not-even-necessary-before-this-change)
includes of <ctype.h>

(cherry picked from commit 0d9b449ae95f26e86f8b433c7f4f99341443b048)

Change-Id: Ic2be240369c62a06bd5152fda46e6ad9027570cf
Reviewed-on: https://code.wireshark.org/review/4869
Reviewed-by: Guy Harris <guy@alum.mit.edu>