OS X Server iOS development certificate removal/renewal

About a year ago, I was experimenting with setting up an Xcode build server on my home server. After the experiments, I turned off the service. More recently, I again activated the service, and it appears at that time Xcode obtained a new set of development certificates. However, the older development certificate is now expiring, and I get a pair of warnings that the that certificate is expiring soon. I have deleted the certificate from the keychain, but I still get the warning. I cannot find any reference to the certificate in the Server app, nor on the attached iOS developer account. Any ideas where I can go to remove this certificate so Server does not give me the warning?