slight tidy-up of /etc/services:

slight tidy-up of /etc/services:

- remove a few UDP entries for protocols that are TCP-only

- drop some obsolete protocols

- move smtps/465 to the standards section (rfc8314)

- move the talk about IANA's "reserve for both UDP/TCP even when you only
use one" policy from a comment in /etc/services to the manual, and talk
about how an entry in /etc/services prevents the associated port from
being used for dynamic ports (via net.inet.udp|tcp.baddynamic sysctl).

ok phessler@ florian@