Revert rust-lang#95993 fix

This reverts the temporary fix implemented by rust-lang#95993 since a permanent fix has been implemented by rust-lang/cargo#10594

src/bootstrap/bin/rustdoc.rs

@@ -31,9 +31,7 @@ fn main() {
 
     let mut cmd = Command::new(rustdoc);
 
-    // cfg(bootstrap)
-    // NOTE: the `--test` special-casing can be removed when https://github.com/rust-lang/cargo/pull/10594 lands on beta.
-    if target.is_some() || args.iter().any(|x| x == "--test") {
+    if target.is_some() {
         // The stage0 compiler has a special sysroot distinct from what we
         // actually downloaded, so we just always pass the `--sysroot` option,
         // unless one is already set.