'SQL Response Alert Repository 1' should be listed in the Add/ Remove Program. But since you are not seeing it in this list .. I would assume that you have installed the Alert Repository on a different machines (and client was on this machine for which you have posted the screen shot).
Do you remember that which machine you installed Alert Repository on? Please log to that machine and then uninstall 'SQL Response Alert Repository'.
But if you do not remember then .. if you have emails coming then look at this part of the email:
More details for Server: Server1/SQL2005 - sqlresponse://machinename.red-gate.com: ... a56acf4b78
This should be the machine machinename.red-gate.com
on which you have installed your Alert Repository.
Hope this helps.