Dedup &mut * reborrow suggestion in loops

[ShE3py]

#73534 added a reborrow suggestion in loops; #127579 generalized this to generic parameters, making the suggestion triggers twice:

use std::io::Read;

fn decode_scalar(_reader: impl Read) {}
fn decode_array(reader: &mut impl Read) {
    for _ in 0.. {
        decode_scalar(reader);
    }
}

error[E0382]: use of moved value: `reader`
 --> src/lib.rs:6:23
  |
4 | fn decode_array(reader: &mut impl Read) {
  |                 ------ move occurs because `reader` has type `&mut impl Read`, which does not implement the `Copy` trait
5 |     for _ in 0.. {
  |     ------------ inside of this loop
6 |         decode_scalar(reader);
  |                       ^^^^^^ value moved here, in previous iteration of loop
  |
help: consider creating a fresh reborrow of `reader` here
  |
6 |         decode_scalar(&mut *reader);
  |                       ++++++
help: consider creating a fresh reborrow of `reader` here
  |
6 |         decode_scalar(&mut *reader);
  |                       ++++++

This PR removes the suggestion in loops, as it requires generic parameters anyway (i.e., the reborrow is automatic if there is no generic params).

@rustbot label +A-borrow-checker +A-diagnostics +A-suggestion-diagnostics +D-papercut

[rustbot]

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