To stop the cross platform tracker from starting and prevent message from coming out, you will need to update the CA 7 initialization file reference by the UCC7IN DD in the CA 7 STC proc. On the XPDEF statement you will need to code XSUBMIT=NO and this will disable internal cross platform scheduling interface for XPJOB and therefore you will not get message.
Also, you will need to comment out or remove the Tracker's checkpoint dataset from the CA 7 STC proc. This is the XCKPT DD statement.
Example:
XPDEF,XSUBMIT=NO