Don't define struct mymsg.

PR:		224299, 224443 (exp-run)
Reviewed by:	kib, jhb
Exp-run by:	antoine
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D14491

sys/sys/msg.h

@@ -101,23 +101,6 @@ struct msqid_ds {
 	time_t	msg_ctime;	/* time of last msgctl() */
 };
 
-#if __BSD_VISIBLE
-/*
- * Structure describing a message.  The SVID doesn't suggest any
- * particular name for this structure.  There is a reference in the
- * msgop man page that reads "The structure mymsg is an example of what
- * this user defined buffer might look like, and includes the following
- * members:".  This sentence is followed by two lines equivalent
- * to the mtype and mtext field declarations below.  It isn't clear
- * if "mymsg" refers to the name of the structure type or the name of an
- * instance of the structure...
- */
-struct mymsg {
-	long	mtype;		/* message type (+ve integer) */
-	char	mtext[1];	/* message body */
-};
-#endif
-
 #ifdef _KERNEL
 struct msg {
 	struct	msg *msg_next;  /* next msg in the chain */