make NoopClient feature dependant (Azure#1380)

Instead of always compiling in NoopClient, make it something that's only available if the reqwest clients were not enabled.

sdk/core/src/http_client/mod.rs

@@ -1,27 +1,30 @@
+#[cfg(not(any(feature = "enable_reqwest", feature = "enable_reqwest_rustls")))]
 mod noop;
 #[cfg(any(feature = "enable_reqwest", feature = "enable_reqwest_rustls"))]
 mod reqwest;
 
+#[cfg(not(any(feature = "enable_reqwest", feature = "enable_reqwest_rustls")))]
+use self::noop::NoopClient;
 #[cfg(any(feature = "enable_reqwest", feature = "enable_reqwest_rustls"))]
-pub use self::reqwest::*;
-pub use noop::*;
-
+use self::reqwest::*;
+use crate::error::ErrorKind;
+use async_trait::async_trait;
+use bytes::Bytes;
+use serde::Serialize;
 use std::sync::Arc;
 
 /// Construct a new `HttpClient`
 pub fn new_http_client() -> Arc<dyn HttpClient> {
-    #[allow(unused)]
-    let http_client: Arc<dyn HttpClient> = Arc::new(NoopClient);
     #[cfg(any(feature = "enable_reqwest", feature = "enable_reqwest_rustls"))]
-    let http_client = new_reqwest_client();
-    http_client
+    {
+        new_reqwest_client()
+    }
+    #[cfg(not(any(feature = "enable_reqwest", feature = "enable_reqwest_rustls")))]
+    {
+        Arc::new(NoopClient)
+    }
 }
 
-use crate::error::ErrorKind;
-use async_trait::async_trait;
-use bytes::Bytes;
-use serde::Serialize;
-
 /// An HTTP client which can send requests.
 #[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
 #[cfg_attr(not(target_arch = "wasm32"), async_trait)]