In d242125 I claimed that `ParseIntError` was somehow special, I no
longer thing this is the case. As we pin down the re-export policy (for
errors and other types) it is hard if we have one non-typical re-export.
We have https://github.com/rust-bitcoin/rust-bitcoin/issues/3068 to
discuss the policy, for now just remove the unusual re-export.
ab581a90f8