conn: Remove assert on new listener connection when retrying

Opening a new listener connection can fail in many ways like a bind()
permission denied on a low port for instance.

And thus, we should expect to handle an error when creating a new one instead
of assert() on it.

To hit the removed assert:

  ORPort 80
  KeepBindCapabilities 0

Start tor. Then edit torrc:

  ORPort <some-IP>:80

HUP tor and the assert is hit.

Fixes #40073

Signed-off-by: David Goulet <dgoulet@torproject.org>