audit: drop the meaningless and format breaking word 'user'

userspace audit messages look like so:

type=USER msg=audit(1271170549.415:24710): user pid=14722 uid=0 auid=500 ses=1 subj=unconfined_u:unconfined_r:auditctl_t:s0-s0:c0.c1023 msg=''

That third field just says 'user'.  That's useless and doesn't follow the
key=value pair we are trying to enforce.  We already know it came from the
user based on the record type.  Kill that word.  Die.
Signed-off-by: NEric Paris <eparis@redhat.com>

kernel/audit.c

@@ -631,7 +631,7 @@ static int audit_log_common_recv_msg(struct audit_buffer **ab, u16 msg_type,
 	}
 
 	*ab = audit_log_start(NULL, GFP_KERNEL, msg_type);
-	audit_log_format(*ab, "user pid=%d uid=%u auid=%u ses=%u",
+	audit_log_format(*ab, "pid=%d uid=%u auid=%u ses=%u",
 			 pid, uid, auid, ses);
 	if (sid) {
 		rc = security_secid_to_secctx(sid, &ctx, &len);