Remove let_chain feature and update logic

Summary:
The unstable let_chains feature was removed in 1.90.0 for editions below 2024.

While this buck target is edition 2024, the `try_stream!` macro is passing a let_chain over to the [async_stream crate](https://www.internalfb.com/code/fbsource/[17267cc0a688cd26890a0f4ad1940ebc87047a3c]/third-party/rust/vendor/async-stream-0.3.5/src/lib.rs?lines=227) which [isn't 2024 edition.](https://www.internalfb.com/code/fbsource/[17267cc0a688cd26890a0f4ad1940ebc87047a3c]/third-party/rust/vendor/async-stream-0.3.5/Cargo.toml?lines=13)

rust-lang/rust#143214

rust-lang/rust#145878

Reviewed By: diliop

Differential Revision: D83312115

fbshipit-source-id: 64d31b4f400e0546d9985b78c6c3fade5598d28c

Author: cjlongoria

eden/mononoke/mercurial/bundles/src/lib.rs

@@ -5,7 +5,6 @@
  * GNU General Public License version 2.
  */
 
-#![feature(let_chains)]
 use mononoke_macros::mononoke;
 pub mod bundle2;
 pub mod bundle2_encode;

eden/mononoke/mercurial/bundles/src/utils.rs

@@ -159,8 +159,13 @@ where
                 yield frame;
             }
         }
-        while !buf.is_empty() && let Some(frame) = decoder.decode_eof(&mut buf)? {
-            yield frame;
+        while !buf.is_empty()
+        {
+            if let Some(frame) = decoder.decode_eof(&mut buf)? {
+                yield frame;
+            } else {
+                break
+            }
         }
     }
 }