Remove unrelated noop module visibility change

This change belongs to PR #4420 (observability metrics) where it's
actually needed for testing, not in the endpoint override metric PR.

Author: vcjana

rust-runtime/aws-smithy-observability/src/lib.rs

@@ -25,8 +25,7 @@ mod error;
 pub use error::{ErrorKind, GlobalTelemetryProviderError, ObservabilityError};
 pub mod global;
 pub mod meter;
-#[doc(hidden)]
-pub mod noop;
+mod noop;
 mod provider;
 pub use provider::{TelemetryProvider, TelemetryProviderBuilder};
 pub mod instruments;