MXS-2012 Remove old replication lag detection

The method was quite disruptive as it continuosly wrote to the database.
Also removed the MaxScale ID global, as it wasn't used for anything else.

include/maxscale/config.h

@@ -245,7 +245,6 @@ typedef struct
     char          release_string[RELEASE_STR_LENGTH]; /**< The release name string of the system */
     char          sysname[SYSNAME_LEN];    /**< The OS name of the system */
     uint8_t       mac_sha1[SHA_DIGEST_LENGTH];         /**< The SHA1 digest of an interface MAC address */
-    unsigned long id;                                  /**< MaxScale ID */
     unsigned int  n_nbpoll;                            /**< Tune number of non-blocking polls */
     unsigned int  pollsleep;                           /**< Wait time in blocking polls */
     int           syslog;                              /**< Log to syslog */