As of 8dd11ae, we have `/dev/tty`, which is used by openssh's built-in
read_passphrase function to access the TTY, making our patch
unnecessary.
Removing it also fixes a subtle issue: we did not handle the case of
stdout not being a TTY correctly, so prompts failed to show up when e.g.
the ssh process was being piped to. This made `git clone` not work when
the server's fingerprint was not already verified.
