Remove re-export of ParseIntError

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.

bitcoin/src/blockdata/script/witness_version.rs

@@ -11,7 +11,7 @@ use core::fmt;
 use core::str::FromStr;
 
 use internals::write_err;
-use units::{parse, ParseIntError};
+use units::parse::{self, ParseIntError};
 
 use crate::opcodes::all::*;
 use crate::opcodes::Opcode;

units/src/lib.rs

@@ -51,7 +51,5 @@ pub use self::amount::{Amount, SignedAmount};
 pub use self::{
     block::{BlockHeight, BlockInterval},
     fee_rate::FeeRate,
-    // ParseIntError is used by other modules, so we re-export it.
-    parse::ParseIntError,
     weight::Weight
 };