python3Packages.setuptools-rust: fix cross build for all setuptools-rust based packages

Prior to this change all python packages using `setuptools-rust` were broken when cross compiled as they built binaries for the build platform instead of for the host platform.

The setuptoolsRustBuildHook hook would have to be included as a native build input instead of the `setuptools-rust` package, but practically wasn't used anywhere.

This change makes it so that `setuptoolsRustBuildHook` becomes unnecessary, and instead `setuptools-rust` propagates a setup-hook directly setting up the build environment, similar to how cmake does it when included via nativeBuildInputs.

This change fixes cross on all packages using `setuptools-rust` as a build-system.

pkgs/development/interpreters/python/hooks/default.nix

@@ -441,20 +441,6 @@ in
     } ./setuptools-build-hook.sh
   ) { };
 
-  setuptoolsRustBuildHook = callPackage (
-    { makePythonHook, setuptools-rust }:
-    makePythonHook {
-      name = "setuptools-rust-setup-hook";
-      propagatedBuildInputs = [ setuptools-rust ];
-      substitutions = {
-        pyLibDir = "${python}/lib/${python.libPrefix}";
-        cargoBuildTarget = stdenv.hostPlatform.rust.rustcTargetSpec;
-        cargoLinkerVar = stdenv.hostPlatform.rust.cargoEnvVarTarget;
-        targetLinker = "${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc";
-      };
-    } ./setuptools-rust-hook.sh
-  ) { };
-
   unittestCheckHook = callPackage (
     { makePythonHook }:
     makePythonHook {

pkgs/development/interpreters/python/hooks/setuptools-rust-hook.sh

@@ -1,20 +0,0 @@
-# shellcheck shell=bash
-
-echo "Sourcing setuptools-rust-hook"
-
-setuptoolsRustSetup() {
-    # This can work only if rustPlatform.cargoSetupHook is also included
-    if ! command -v cargoSetupPostPatchHook >/dev/null; then
-        echo "ERROR: setuptools-rust has to be used alongside with rustPlatform.cargoSetupHook!"
-        exit 1
-    fi
-
-    export PYO3_CROSS_LIB_DIR="@pyLibDir@"
-    export CARGO_BUILD_TARGET=@cargoBuildTarget@
-    # TODO theoretically setting linker should not be required because it is
-    # already set in pkgs/build-support/rust/hooks/default.nix but build fails
-    # on missing linker without this.
-    export CARGO_TARGET_@cargoLinkerVar@_LINKER=@targetLinker@
-}
-
-preConfigureHooks+=(setuptoolsRustSetup)