Deprecation/Removal of /master/shutdown endpoint

[Jörg Schad]

Hi,
just as a short reminder: With 0.23 we deprecated the /master/shutdown in
favor of the more consistent /master/teardown endpoint. See MESOS-2697 for
details.

With Mesos 0.24 we will remove the /master/shutdown endpoint completely.

Thanks!
Joerg