Update to 8.0.16

Upstream has unbundled all of the 3rd party jars they used to ship in
the tarball. We already preferred installing slf4j.jar and c3p0.jar
from ports, so we just had to add a dependency (and create a port for)
protobuf-java.jar

ChangeLog: https://dev.mysql.com/doc/relnotes/connector-j/8.0/en/news-8-0-16.html