MINOR: server: unmark deprecated on enable health/agent cli

MINOR: server: unmark deprecated on enable health/agent cli

Remove the "DEPRECATED" marker on "enable/disable health/agent"
commands. Their purpose is to toggle the check/agent on a server.

These commands are still useful because their purpose is not covered by
the "set server" command. Most there was confusion with the commands
'set server health/agent', which in fact serves another goal.

Note that the indication "use 'set server' instead" has been added since
2016 on the commit
  2c04eda8b58636ad2ae44e42b1f50f3b5a24a642
  REORG: cli: move "{enable|disable} health" to server.c

and
  58d9cb7d22c1b0d8239543443131e3e3658375d0
  REORG: cli: move "{enable|disable} agent" to server.c

Besides, these commands will become required to enable check/agent on
dynamic servers which will be created with check disabled.

This should be backported up to 2.4.