Remove deprecated SSH-related commands from the client

[anayden]

This PR addresses client-side component of neuro-inc/platform-api#515

Removing the neuro model command, the neuro config id_rsa subcommand and the neuro job submit --ssh option.

• The whole neuro model command has been deprecated for a few months.
• neuro job submit --ssh has been deprecated for a few months as well.
• neuro config id_rsa has been hidden for quite a while and has no use cases without the commands above.

[dalazx]

@truskovskiyk fyi

[dalazx]

@anayden awesome!

should we update the changelog?
cc @asvetlov

[asvetlov]

Yes, sure.
The change worth CHANGELOG record

[codecov]

Codecov Report

Merging #700 into master will increase coverage by 1.75%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #700      +/-   ##
==========================================
+ Coverage   90.43%   92.19%   +1.75%     
==========================================
  Files          40       39       -1     
  Lines        3230     3112     -118     
  Branches      445      437       -8     
==========================================
- Hits         2921     2869      -52     
+ Misses        237      179      -58     
+ Partials       72       64       -8

Impacted Files	Coverage Δ
neuromation/cli/ssh_utils.py	0% <ø> (-19.15%)	⬇️
neuromation/cli/config.py	87.5% <ø> (+0.48%)	⬆️
neuromation/cli/formatters/config.py	100% <ø> (ø)	⬆️
neuromation/api/models.py	96.29% <100%> (-3.71%)	⬇️
neuromation/cli/job.py	92.22% <100%> (+1.54%)	⬆️
neuromation/cli/rc.py	93.4% <100%> (+0.86%)	⬆️
neuromation/api/jobs.py	93.42% <100%> (+0.22%)	⬆️
neuromation/cli/main.py	60.71% <100%> (+0.3%)	⬆️
... and 9 more

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