libc/syslog: fully deprecate and don't try to open "/dev/log"

The "/dev/log" socket existed in pre-FreeBSD times.  Later it was
substituted to a compatibility symlink.  The symlink creation was
deprecated in FreeBSD 10.2 and 9-STABLE.

Reviewed by:		markj
Differential revision:	https://reviews.freebsd.org/D35304

lib/libc/gen/syslog.c

@@ -435,18 +435,6 @@ connectlog(void)
 				status = CONNDEF;
 		}
 
-		if (status == NOCONN) {
-			/*
-			 * Try the old "/dev/log" path, for backward
-			 * compatibility.
-			 */
-			(void)strncpy(SyslogAddr.sun_path, _PATH_OLDLOG,
-			    sizeof SyslogAddr.sun_path);
-			if (_connect(LogFile, (struct sockaddr *)&SyslogAddr,
-			    sizeof(SyslogAddr)) != -1)
-				status = CONNDEF;
-		}
-
 		if (status == NOCONN) {
 			(void)_close(LogFile);
 			LogFile = -1;

sys/sys/syslog.h

@@ -37,7 +37,6 @@
 
 #define	_PATH_LOG	"/var/run/log"
 #define	_PATH_LOG_PRIV	"/var/run/logpriv"
-#define	_PATH_OLDLOG	"/dev/log"	/* backward compatibility */
 
 /*
  * priorities/facilities are encoded into a single 32-bit quantity, where the