Comment out the <serviceCredentials> section (add the <!-- and --> to the beginning and end of the attribute).
<!--<serviceCredentials>-->
<!-- Select the certificate to use for Message Security here.-->
<!--<serviceCertificate findValue="[CertificateSubjectName]"
storeLocation="LocalMachine"
storeName="My"
x509FindType="FindBySubjectName" />
</serviceCredentials>-->