mon/MonCommands: remove obsolete mds commands

mon/MonCommands: remove obsolete mds commands

* "mds dump"
  "mds getmap",
  "mds stop",
  "mds set_max_mds",
  "mds set",
  "mds rmfailed"
  "mds add_data_pool"
  "mds rm_data_pool"
  "mds remove_data_pool"
  the commands above were marked "OBSOLETE" back in
  a8fc92933bb24fe8ed06407335746f1262d6aea8, which was included in v13.0.1,
* "mds tell" was marked obsolete in
  e0d1127205bb45bb623a50b4b68ae85f7b083e04, which was included in v12.0.2,
* "mds deactivate" was marked obsolete in
  c7bd6f02c74513f29be12ae47808ca1a1ddaec9f, which was included in v13.1.0,
* "mds newfs" was marked obsolete in
  072c41e3492a13525d2a45465ed580fc1426fbd1, which was included by v12.0.2

so according to our command retirement policy proposed by
https://ceph-users.ceph.narkive.com/iUh4e0nj/rfc-deprecating-ceph-tool-commands

> Once two major releases go by, the command will then enter the OBSOLETE
> period. This would be one major release, during which the command would
> no longer work although still acknowledged. A simple message down the
> lines of 'This command is now obsolete; please check the docs' would
> suffice to inform the user.

since the next release will be v17. it's been long enough for retiring
these OBSOLETE commands.

Signed-off-by: Kefu Chai <kchai@redhat.com>