curses: build fix for italics attribute support

I've been building tty-only for a while in order to speed up
builds, so a recent change to the curses interface that broke
compile on older OSX went unnoticed.  The <curses.h> on my
OSX 10.11.6 system does not define A_ITALIC.

win/curses/cursmisc.c

@@ -12,10 +12,6 @@
 
 #include <ctype.h>
 
-#ifndef A_ITALIC
-#define A_ITALIC A_UNDERLINE
-#endif
-
 /* Misc. curses interface functions */
 
 /* Private declarations */