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>

Change-Id: I1384e3ae4ccba6af9220a08773abcde7ea320573
Reviewed-on: https://code.wireshark.org/review/4755
Reviewed-by: Guy Harris <guy@alum.mit.edu>