hw/xwin: Fix redundant declaration warning in winprefslex.l

winprefslex.l:40:12: warning: redundant redeclaration of ‘yyparse’ [-Wredundant-decls]
winprefsyacc.h:130:5: note: previous declaration of ‘yyparse’ was here

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>

hw/xwin/winprefslex.l

@@ -37,8 +37,6 @@
 #include <string.h>
 #include "winprefsyacc.h"
 
-extern int yyparse(void);
-
 extern void ErrorF (const char* /*f*/, ...);
 
 /* Copy the parsed string, must be free()d in yacc parser */