Revert let_chains stabilization

This reverts commit 3266460.

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

Author: Noratrieb

Diff for: clippy_dev/src/lib.rs

@@ -1,3 +1,4 @@
+#![feature(let_chains)]
 #![feature(let_else)]
 #![feature(once_cell)]
 #![feature(rustc_private)]

Diff for: clippy_lints/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(control_flow_enum)]
 #![feature(drain_filter)]
 #![feature(iter_intersperse)]
+#![feature(let_chains)]
 #![feature(let_else)]
 #![feature(lint_reasons)]
 #![feature(never_type)]

Diff for: clippy_utils/src/lib.rs

@@ -2,6 +2,7 @@
 #![feature(box_patterns)]
 #![feature(control_flow_enum)]
 #![feature(let_else)]
+#![feature(let_chains)]
 #![feature(lint_reasons)]
 #![feature(once_cell)]
 #![feature(rustc_private)]

Diff for: tests/ui/needless_late_init.fixed

@@ -1,4 +1,5 @@
 // run-rustfix
+#![feature(let_chains)]
 #![allow(
     unused,
     clippy::assign_op_pattern,

Diff for: tests/ui/needless_late_init.rs

@@ -1,4 +1,5 @@
 // run-rustfix
+#![feature(let_chains)]
 #![allow(
     unused,
     clippy::assign_op_pattern,

Diff for: tests/ui/needless_late_init.stderr

@@ -1,5 +1,5 @@
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:22:5
+  --> $DIR/needless_late_init.rs:23:5
    |
 LL |     let a;
    |     ^^^^^^ created here
@@ -13,7 +13,7 @@ LL |     let a = "zero";
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:25:5
+  --> $DIR/needless_late_init.rs:26:5
    |
 LL |     let b;
    |     ^^^^^^ created here
@@ -27,7 +27,7 @@ LL |     let b = 1;
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:26:5
+  --> $DIR/needless_late_init.rs:27:5
    |
 LL |     let c;
    |     ^^^^^^ created here
@@ -41,7 +41,7 @@ LL |     let c = 2;
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:30:5
+  --> $DIR/needless_late_init.rs:31:5
    |
 LL |     let d: usize;
    |     ^^^^^^^^^^^^^ created here
@@ -54,7 +54,7 @@ LL |     let d: usize = 1;
    |     ~~~~~~~~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:33:5
+  --> $DIR/needless_late_init.rs:34:5
    |
 LL |     let e;
    |     ^^^^^^ created here
@@ -67,7 +67,7 @@ LL |     let e = format!("{}", d);
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:38:5
+  --> $DIR/needless_late_init.rs:39:5
    |
 LL |     let a;
    |     ^^^^^^
@@ -88,7 +88,7 @@ LL |     };
    |      +
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:47:5
+  --> $DIR/needless_late_init.rs:48:5
    |
 LL |     let b;
    |     ^^^^^^
@@ -109,7 +109,7 @@ LL |     };
    |      +
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:54:5
+  --> $DIR/needless_late_init.rs:55:5
    |
 LL |     let d;
    |     ^^^^^^
@@ -130,7 +130,7 @@ LL |     };
    |      +
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:62:5
+  --> $DIR/needless_late_init.rs:63:5
    |
 LL |     let e;
    |     ^^^^^^
@@ -151,7 +151,7 @@ LL |     };
    |      +
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:69:5
+  --> $DIR/needless_late_init.rs:70:5
    |
 LL |     let f;
    |     ^^^^^^
@@ -167,7 +167,7 @@ LL +         1 => "three",
    |
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:75:5
+  --> $DIR/needless_late_init.rs:76:5
    |
 LL |     let g: usize;
    |     ^^^^^^^^^^^^^
@@ -187,7 +187,7 @@ LL |     };
    |      +
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:83:5
+  --> $DIR/needless_late_init.rs:84:5
    |
 LL |     let x;
    |     ^^^^^^ created here
@@ -201,7 +201,7 @@ LL |     let x = 1;
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:87:5
+  --> $DIR/needless_late_init.rs:88:5
    |
 LL |     let x;
    |     ^^^^^^ created here
@@ -215,7 +215,7 @@ LL |     let x = SignificantDrop;
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:91:5
+  --> $DIR/needless_late_init.rs:92:5
    |
 LL |     let x;
    |     ^^^^^^ created here
@@ -229,7 +229,7 @@ LL |     let x = SignificantDrop;
    |     ~~~~~
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:110:5
+  --> $DIR/needless_late_init.rs:111:5
    |
 LL |     let a;
    |     ^^^^^^
@@ -250,7 +250,7 @@ LL |     };
    |      +
 
 error: unneeded late initialization
-  --> $DIR/needless_late_init.rs:127:5
+  --> $DIR/needless_late_init.rs:128:5
    |
 LL |     let a;
    |     ^^^^^^