Stabilize --crate-version option in rustdoc

src/bootstrap/bin/rustdoc.rs

@@ -52,12 +52,7 @@ fn main() {
     // Bootstrap's Cargo-command builder sets this variable to the current Rust version; let's pick
     // it up so we can make rustdoc print this into the docs
     if let Some(version) = env::var_os("RUSTDOC_CRATE_VERSION") {
-        // This "unstable-options" can be removed when `--crate-version` is stabilized
-        if !has_unstable {
-            cmd.arg("-Z").arg("unstable-options");
-        }
         cmd.arg("--crate-version").arg(version);
-        has_unstable = true;
     }
 
     // Needed to be able to run all rustdoc tests.