Remove keys-gen app

[mrpalide]

Fixes: #7

Changes:

• remove key-gens cmd app

Description:
address-gen on Skycoin needs a little fix (missing label value), also I add new flag -key-pairs to printout only key pairs there. So if we can merge related PR on Skycoin (skycoin/skycoin#2713) we can merge this PR too. Otherwise, we should close both of them and keep key-gens here.

[0pcom]

I will note that the functionality of keys-gen is duplicated for skywire-cli config gen-keys

However, I'm uncertain that we should remove it. What is the suggested alternative method for doing this? I would just hate to make an inconvenient situation for future developers where they needed to look in a different repo for this utility.

Note also that some documentation may reflect the use of keys-gen. So that documentation may need be changed (check skywire-deployment repo) if this utility is removed.

I might suggest simply relocating it from cmd/ to some subdirectory of examples/ - just in case / for convenience.

Unless there is another easy way to do this that i'm missing.

[0pcom]

on second thought, i suggest move keys-gen to skywire-utilities. I think that is an appropriate place for it.