ipcheck: Drop the "Rust (New)" implementation

There have been no substantial changes in implementation of various
Rust's IpAddr helper methods (is_loopback() etc.) that I can think of.

The PR[1] that the "Rust (New)" implementation was based on has been
closed in May 2021, I think it's safe to say it's no longer relevant
and doesn't help anyone.

[1] rust-lang/rust#76098

tools/ipcheck/README.md

@@ -1,6 +1,7 @@
 # IP Check
 
-Created for https://github.com/rust-lang/rust/pull/76098
+Originally created for https://github.com/rust-lang/rust/pull/76098, the tool now tests
+the *current* implementation of various helper methods against other programming languages.
 
 This is a little utility program for checking the behavior of various language's IP address implementations.
 The goal is to make sure the Rust programs are either the same or deliberately different to other languages.
@@ -11,13 +12,15 @@ This same approach might be useful for other APIs that have externally specified
 
 These live under the `impls` directory.
 
-- Rust (New) (`impls/rust`) with the behavior proposed in `#76098`
 - Rust (Current) (`impls/rust_current`) with the current behavior on `nightly`
 - .NET (`impls/dotnet`)
 - Python (`impls/python`)
 - Go (`impls/go`)
 - Java (`impls/java`)
 
+There was a Rust implementation with behavior proposed in `#76098` ("Rust (New)")
+but the PR didn't go through so the implementation has been removed.
+
 ## Running
 
 With the comparison languages available, you can run `cd host && cargo run` to compare them.

tools/ipcheck/host/build/build.rs

@@ -12,8 +12,7 @@ fn main() {
     let mut impls =
         std::fs::File::create("../artifacts/.impls").expect("failed to create .impls file");
 
-    output_impl(&mut impls, "Rust (New)", rust::build_new());
-    output_impl(&mut impls, "Rust (Current)", rust::build_current());
+    output_impl(&mut impls, "Rust", rust::build_current());
     output_impl(&mut impls, ".NET", dotnet::build());
     output_impl(&mut impls, "Python", python::build());
     output_impl(&mut impls, "Go", go::build());

tools/ipcheck/host/build/rust.rs

@@ -1,9 +1,5 @@
 use std::path::Path;
 
-pub fn build_new() -> std::io::Result<String> {
-    build_bin("../impls/rust_new", "../artifacts/rust_new", "ipcheck_new")
-}
-
 pub fn build_current() -> std::io::Result<String> {
     build_bin(
         "../impls/rust_current",

tools/ipcheck/host/main.rs

@@ -1,7 +1,7 @@
 use serde_json::{Map, Value};
 use std::{collections::BTreeSet, fmt::Write, io::BufRead, net::IpAddr};
 
-const REF_LANG: &'static str = "Rust (New)";
+const REF_LANG: &'static str = "Rust";
 
 fn is_ref(lang: &str) -> bool {
     lang.starts_with("Rust")

tools/ipcheck/impls/README.md

@@ -1,9 +1,8 @@
 Programs that accept as input a ASCII-encoded IP address to parse and run operations on. As output, these programs produce a JSON object.
 
 ## Implementations
- - Rust (`rust_*`) (with the behavior specified in https://github.com/rust-lang/rust/pull/76098 as `rust_new`)
+ - Rust (`rust`)
  - .NET (`dotnet`)
  - Python (`python`)
  - Go (`go`)
  - Java (`java`)
-