revert upstreams dog fooding to be able to keep our rust package small
and lib*.rmeta and lib*.so in the split rustc-dev subpackage,
see 64e07cc011202de8f04468ed04db82ee30055aa3

upstream change that introduced this:

https://github.com/rust-lang/rust/commit/b2a322beb29110e22a1782e2ce5ed2a0719b81ed

--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -1095,10 +1095,6 @@ impl Builder<'_> {
         // Enable usage of unstable features
         cargo.env("RUSTC_BOOTSTRAP", "1");
 
-        if matches!(mode, Mode::Std) {
-            cargo.arg("-Zno-embed-metadata");
-        }
-
         if self.config.dump_bootstrap_shims {
             prepare_behaviour_dump_dir(self.build);