remove let_chain feature

Summary:
X-link: meta-pytorch/monarch#1388

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

fbshipit-source-id: 6fb40aa7e1c282f453394db5b7f0dab1282c2e35

Author: cjlongoria

crates/pyrefly_build/src/lib.rs

@@ -25,7 +25,6 @@
 #![deny(clippy::trivially_copy_pass_by_ref)]
 #![feature(const_type_name)]
 #![feature(if_let_guard)]
-#![feature(let_chains)]
 
 use std::path::PathBuf;
 

crates/pyrefly_python/src/lib.rs

@@ -17,7 +17,6 @@
 #![deny(clippy::string_to_string)]
 #![deny(clippy::trivially_copy_pass_by_ref)]
 #![feature(if_let_guard)]
-#![feature(let_chains)]
 
 pub mod ast;
 pub mod display;

crates/pyrefly_types/src/lib.rs

@@ -21,7 +21,6 @@
 #![deny(clippy::trivially_copy_pass_by_ref)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
-#![feature(let_chains)]
 
 pub mod alias;
 pub mod annotation;

crates/pyrefly_util/src/lib.rs

@@ -25,7 +25,6 @@
 #![deny(clippy::trivially_copy_pass_by_ref)]
 #![feature(const_type_name)]
 #![feature(if_let_guard)]
-#![feature(let_chains)]
 
 //! Utility functions that are not specific to the things Pyre does.
 

pyrefly/lib/lib.rs

@@ -27,7 +27,6 @@
 #![feature(box_patterns)]
 #![feature(closure_lifetime_binder)]
 #![feature(if_let_guard)]
-#![feature(let_chains)]
 
 mod alt;
 mod binding;