Mosh should unset SSH_TTY when initialized over ssh

[carloscabanero]

There is a mosh PR to do this on the server side, but I think we can fix this on the client side as it is the one responsible for the "dropped" ssh connection: https://github.com/mobile-shell/mosh/pull/1187

More context here: https://discord.com/channels/441939332442619905/859725438359830578/1196936949261418537 and: https://discord.com/channels/441939332442619905/442378162425298954/1204931530351321158

Also original issue: https://github.com/spudlyo/clipetty/issues/9