Rollup merge of #86517 - camsteffen:unused-unsafe-async, r=LeSeulArtichaut

Fix `unused_unsafe` around `await`

Enables `unused_unsafe` lint for `unsafe { future.await }`.

The existing test for this is `unsafe { println!() }`, so I assume that `println!` used to contain compiler-generated unsafe but this is no longer true, and so the existing test is broken. I replaced the test with `unsafe { ...await }`. I believe `await` is currently the only instance of compiler-generated unsafe.

Reverts some parts of #85421, but the issue predates that PR.

src/test/ui/unsafe/unsafe-around-compiler-generated-unsafe.mir.stderr

@@ -1,11 +1,11 @@
 error: unnecessary `unsafe` block
-  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:9:5
+  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:9:9
    |
-LL |     unsafe { println!("foo"); }
-   |     ^^^^^^ unnecessary `unsafe` block
+LL |         unsafe { async {}.await; }
+   |         ^^^^^^ unnecessary `unsafe` block
    |
 note: the lint level is defined here
-  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:6:9
+  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:5:9
    |
 LL | #![deny(unused_unsafe)]
    |         ^^^^^^^^^^^^^

src/test/ui/unsafe/unsafe-around-compiler-generated-unsafe.rs

@@ -1,10 +1,11 @@
-// issue #12418
-
+// edition:2018
 // revisions: mir thir
 // [thir]compile-flags: -Z thir-unsafeck
 
 #![deny(unused_unsafe)]
 
 fn main() {
-    unsafe { println!("foo"); } //~ ERROR unnecessary `unsafe`
+    let _ = async {
+        unsafe { async {}.await; } //~ ERROR unnecessary `unsafe`
+    };
 }

src/test/ui/unsafe/unsafe-around-compiler-generated-unsafe.thir.stderr

@@ -1,11 +1,11 @@
 error: unnecessary `unsafe` block
-  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:9:5
+  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:9:9
    |
-LL |     unsafe { println!("foo"); }
-   |     ^^^^^^ unnecessary `unsafe` block
+LL |         unsafe { async {}.await; }
+   |         ^^^^^^ unnecessary `unsafe` block
    |
 note: the lint level is defined here
-  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:6:9
+  --> $DIR/unsafe-around-compiler-generated-unsafe.rs:5:9
    |
 LL | #![deny(unused_unsafe)]
    |         ^^^^^^^^^^^^^