cli: remove --dev mode

[petermattis]

Once #4269 goes in, the only remaining reason for --dev mode is to automatically configure a memory store. I think we should encourage developers (primarily ourselves) to use a disk store instead. See also #4335. Using a disk store during ad-hoc testing is closer to how cockroach will be used in production and will possibly reveal bugs that are not present when always starting from a clean slate.

[tamird]

There is at least one other reason for --dev which I proposed here.

[petermattis]

The discussion in #4269 proposes to make listening on only localhost the default unless --insecure or --{cert,key}-file are specified. I think that covers your proposed usage. Effectively, the lack of --insecure or --{cert,key}-file causes a server to be in dev-mode.

[tamird]

OK, I think that can work.

[petermattis]

Fixed by #4453.