sys: depreacate PTY module, moves to termproxy directly

As termproxy only used this module from the huge proxmox-sys crate,
and this module was also only used here, it makes sense to move it
over there (and dropping proxmox-sys halved build-time from 8.5 s to
4.2 s).

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

proxmox-sys/src/linux/pty.rs

@@ -48,6 +48,7 @@ ioctl_write_ptr_bad!(set_size, libc::TIOCSWINSZ, nix::pty::Winsize);
 ///     Ok(())
 ///  }
 /// ```
+#[deprecated(note="moved to termproxy directly, only used there. Holler if you run into this.")]
 pub struct PTY {
     primary: PtyMaster,
 }