remove let_chain feature (#1388)

Summary:

let_chains were stabilized in 1.88.0 for edition 2024 and removed in 1.90.0
rust-lang/rust#132833
rust-lang/rust#143214

Reviewed By: dtolnay

Differential Revision: D83221093

Author: cjlongoria

hyperactor/src/lib.rs

@@ -65,7 +65,6 @@
 #![feature(panic_update_hook)]
 #![feature(type_alias_impl_trait)]
 #![feature(trait_alias)]
-#![feature(let_chains)]
 #![deny(missing_docs)]
 
 pub mod accum;

hyperactor_mesh/src/lib.rs

@@ -11,7 +11,6 @@
 #![feature(assert_matches)]
 #![feature(exit_status_error)]
 #![feature(impl_trait_in_bindings)]
-#![feature(let_chains)]
 
 pub mod actor_mesh;
 pub mod alloc;