Disabling REPL echo in Unix port

[aivarannamaa]

When I do `stty -echo` either in the shell before starting `python3` or as `os.system("stty -echo")`, the REPL stops local echoing.

Neither of this works with `micropython`. Is this a bug or feature?

I know that bare-metal ports include Raw-REPL, which doesn't echo, but this is missing from the Unix port.