nixos/zsh: Fix tramp support

For a long time, TRAMP has not worked with ZSH NixOS servers. I
thought I fixed this in 0740f57e63af61694d14796286cb9204, but now
realize that was only half the problem. For TRAMP to start working
again ‘unsetopt zle’ was needed, otherwise the connection would hang.
In addition, I have a few more settings added that can apparenty
interfere with these settings.