Remove caveats related to format_args! expansion

The behavior of `format_args!`, with respect to `super let`, had some
caveats that we can remove now that Rust [#145880] has landed, so
let's remove our remarks on that and simplify the tests accordingly.

[#145880]: rust-lang/rust#145880

Author: traviscross

src/destructors.md

@@ -540,9 +540,7 @@ let x = pin!(temp()); // Super operand of super macro call expression.
 # x;
 let x = pin!({ &mut temp() }); // As above.
 # x;
-# // FIXME: Simplify after this PR lands:
-# // <https://github.com/rust-lang/rust/pull/145882>.
-let x = format_args!("{:?}{:?}", (), temp()); // As above.
+let x = format_args!("{:?}", temp()); // As above.
 # x;
 //
 // All of the temporaries above are still live here.
@@ -613,11 +611,10 @@ let x = 'a: { break 'a &temp() }; // ERROR
 pin!({ &temp() }); // ERROR
 ```
 
-<!-- FIXME: Simplify after https://github.com/rust-lang/rust/pull/145882 lands. -->
 ```rust,edition2024,compile_fail,E0716
 # fn temp() {}
 // As above.
-format_args!("{:?}{:?}", (), { &temp() }); // ERROR
+format_args!("{:?}", { &temp() }); // ERROR
 ```
 
 r[destructors.forget]

src/expressions.md

@@ -270,30 +270,22 @@ r[expr.super-macros.format_args]
 r[expr.super-macros.format_args.super-operands]
 Except for the format string argument, all arguments passed to [`format_args!`] are *super operands*.
 
-<!-- FIXME: Remove after https://github.com/rust-lang/rust/pull/145882 lands. -->
-> [!NOTE]
-> When there is only one placeholder, `rustc` does not yet treat the corresponding argument as a super operand. This is a bug.
->
-> For details, see Rust issue [#145880](https://github.com/rust-lang/rust/issues/145880).
-
-<!-- FIXME: Simplify after https://github.com/rust-lang/rust/pull/145882 lands. -->
 ```rust,edition2024
 # fn temp() -> String { String::from("") }
 // Due to the call being an extending expression and the argument
 // being a super operand, the inner block is an extending expression,
 // so the scope of the temporary created in its trailing expression
 // is extended.
-let _ = format_args!("{:?}{}", (), { &temp() }); // OK
+let _ = format_args!("{}", { &temp() }); // OK
 ```
 
 r[expr.super-macros.format_args.super-temporaries]
 The super operands of [`format_args!`] are [implicitly borrowed] and are therefore [place expression contexts]. When a [value expression] is passed as an argument, it creates a *super temporary*.
 
-<!-- FIXME: Simplify after https://github.com/rust-lang/rust/pull/145882 lands. -->
 ```rust
 # fn temp() -> String { String::from("") }
-let x = format_args!("{}{}", temp(), temp());
-x; // <-- The temporaries are extended, allowing use here.
+let x = format_args!("{}", temp());
+x; // <-- The temporary is extended, allowing use here.
 ```
 
 The expansion of a call to [`format_args!`] sometimes creates other internal *super temporaries*.