Remove unnecessary inclusions of <numbers.h>

Functions display_msg() and check_sync() are only used in numbers.c, so they
can be static.

Remove inclusions of <numbers.h> from .c files that don't need it.

include/numbers.h

@@ -14,8 +14,6 @@
 #define __numbers_h_
 
 char *numeric_banner(void);
-void display_msg(char *, char **);
 void numbered_command(char *, int, char **);
-int check_sync(int, char *, char *, char *, char *, ChannelList *);
 		
 #endif /* __numbers_h_ */