post https://example.com/UserMgmt/RemoveUserCertificate
Specified user must be you or you must be a system administrator or have user management permissions.
'certType' will be ignored if 'thumbprint' is specified.
If 'thumbprint' is null, all certs of 'cerType' for the user are removed.
If both 'thumbprint' and 'certType' are null, all certificates for the user are removed.