Yes it is from the legacy SSO (port 7444), I am guessing your vCenter was upgraded all the way from 5.5 - It does not serve any purposes in 7.0. 

I would suggest you to just backup the cert and key just in case and delete the store with the cert. You can do all that by executing following

/usr/lib/vmware-vmafd/bin/vecs-cli entry getcert --store STS_INTERNAL_SSL_CERT --alias __MACHINE_CERT --output /var/tmp/STS_INTERNAL.crt

/usr/lib/vmware-vmafd/bin/vecs-cli entry getkey --store STS_INTERNAL_SSL_CERT --alias __MACHINE_CERT --output /var/tmp/STS_INTERNAL.key

Finally delete the store using:

/usr/lib/vmware-vmafd/bin/vecs-cli store delete --name STS_INTERNAL_SSL_CERT

Hope that helps.