Stop embedding build-time environment variables in _sysconfigdata (#8813)

crates/vm/build.rs wrote every environment variable of the build
process into OUT_DIR/env_vars.rs, and _sysconfigdata included that file
into build_time_vars. All build-machine environment variables ended up
as string literals in the binary and were readable at runtime through
sysconfig.get_config_vars().

Remove the dump and the include, and drop the now unused itertools
build-dependency. build_time_vars keeps only the explicit entries.

Fixes #8802

Assisted-by: Claude:claude-fable-5-1

crates/vm/Cargo.toml

@@ -91,7 +91,6 @@ wasm-bindgen = { workspace = true, optional = true }
 
 [build-dependencies]
 glob = { workspace = true }
-itertools = { workspace = true }
 jiff = { workspace = true }
 
 [lints]

crates/vm/build.rs

@@ -3,12 +3,9 @@
     reason = "build scripts cannot use rustpython-host_env"
 )]
 
-use itertools::Itertools;
 use jiff::{Timestamp, Zoned, tz::TimeZone};
 use std::{
-    env,
-    io::{self, prelude::*},
-    path::PathBuf,
+    env, io,
     process::Command,
     time::{SystemTime, UNIX_EPOCH},
 };
@@ -53,16 +50,6 @@ fn main() {
         "cargo:rustc-env=RUSTPYTHON_TARGET_TRIPLE={}",
         env::var("TARGET").unwrap()
     );
-
-    let mut env_path = PathBuf::from(env::var_os("OUT_DIR").unwrap());
-    env_path.push("env_vars.rs");
-    let mut f = std::fs::File::create(env_path).unwrap();
-    write!(
-        f,
-        "sysvars! {{ {} }}",
-        std::env::vars_os().format_with(", ", |(k, v), f| f(&format_args!("{k:?} => {v:?}")))
-    )
-    .unwrap();
 }
 
 fn git_hash() -> String {

crates/vm/src/stdlib/_sysconfigdata.rs

@@ -69,7 +69,6 @@ mod _sysconfigdata {
             "BASECFLAGS" => "",
             "BLDSHARED" => "cc -shared",
         }
-        include!(concat!(env!("OUT_DIR"), "/env_vars.rs"));
         vars
     }
 }