Revert let_chains stabilization

This reverts commit 3266460749.

This is the revert against master, the beta revert was already done in #100538.

compiler/rustc_feature/src/accepted.rs

@@ -188,8 +188,6 @@ declare_features! (
     (accepted, item_like_imports, "1.15.0", Some(35120), None),
     /// Allows `'a: { break 'a; }`.
     (accepted, label_break_value, "CURRENT_RUSTC_VERSION", Some(48594), None),
-    /// Allows `if/while p && let q = r && ...` chains.
-    (accepted, let_chains, "1.64.0", Some(53667), None),
     /// Allows `break {expr}` with a value inside `loop`s.
     (accepted, loop_break_value, "1.19.0", Some(37339), None),
     /// Allows use of `?` as the Kleene "at most one" operator in macros.

compiler/rustc_feature/src/active.rs

@@ -422,6 +422,8 @@ declare_features! (
     (active, isa_attribute, "1.48.0", Some(74727), None),
     // Allows setting the threshold for the `large_assignments` lint.
     (active, large_assignments, "1.52.0", Some(83518), None),
+    /// Allows `if/while p && let q = r && ...` chains.
+    (active, let_chains, "1.37.0", Some(53667), None),
     /// Allows `let...else` statements.
     (active, let_else, "1.56.0", Some(87335), None),
     /// Allows `#[link(..., cfg(..))]`.