remove local kssh config file

[mmou]

with moving the kssh config file from KBFS to the KV store, we may not need the client config file for improving performance, so we should consider removing this complexity.

maybe i'm missing something, but with this no longer an issue, there's really not much value to having a client config file at all. all of that persistent state isn't nearly as valuable as the added complexity of having some configs sometimes in a file and getting them there and checking for them. the way this thing is used, most people are going to be hitting the same servers and the same bot every time, so if kssh only exposed kssh --bot yourcabot <rest of command> in the event you were in multiple teams with ca-bots, you just write your own alias once (e.g. kssh-prod) and never think about it again, and then kssh gets the added benefit of being basically stateless (excepting your non-kssh ssh configs).

not a task for this PR. but the move from kbfs->kvstore seems like it offers some additional opportunities.

Originally posted by @xgess in https://github.com/keybase/bot-sshca/pull/97