Don't suggest calling `.iter()` when unsatified `Iterator` bound does not originate from an expression

[kennytm]

Demo:

struct S<I: Iterator>(I);
struct T(S<u8>);
fn main() {}

This will cause the strange suggestion:

error[E0277]: the trait bound `u8: std::iter::Iterator` is not satisfied
 --> src/main.rs:2:10
  |
2 | struct T(S<u8>);
  |          ^^^^^^ `u8` is not an iterator; maybe try calling `.iter()` or a similar method
  |
  = help: the trait `std::iter::Iterator` is not implemented for `u8`
note: required by `S`
 --> src/main.rs:1:1
  |
1 | struct S<I: Iterator>(I);
  | ^^^^^^^^^^^^^^^^^^^^^^^^^

There is no place to "call .iter()". That suggestion should be removed here.