fixup build for platforms without curses after drawing.c split

An Undefined reference to decgraphics_mode_callback was possible
if built for tty only.

drawing.c had an #include "tcap.h" which is what actually defined
TERMLIB. It isn't needed in drawing.c anymore, but it is needed
in symbols.c, in order to get the define for TERMLIB so that
decgraphics_mode_callback variable gets defined.

The undefined reference was from win/tty/termcap.h in code that
was #ifdef TERMLIB, but win/tty/termcap.h has the #include "tcap.h"

src/drawing.c

@@ -7,7 +7,6 @@
 #include "rm.h"
 #include "objclass.h"
 #include "monsym.h"
-#include "tcap.h"
 
 /* Relevant header information in rm.h, objclass.h, and monsym.h. */
 

src/symbols.c

@@ -3,6 +3,7 @@
 /* NetHack may be freely redistributed.  See license for details. */
 
 #include "hack.h"
+#include "tcap.h"
 
 extern const uchar def_r_oc_syms[MAXOCLASSES];      /* drawing.c */
 

win/tty/termcap.c

@@ -355,7 +355,7 @@ int state;
 }
 
 #ifdef TERMLIB
-extern void NDECL((*decgraphics_mode_callback)); /* defined in drawing.c */
+extern void NDECL((*decgraphics_mode_callback)); /* defined in symbols.c */
 static void NDECL(tty_decgraphics_termcap_fixup);
 
 /*