Fixes #6540. Also remove a fixme for #2619 since it's not relevant anymore.

…al, r=dswij

Add new lint [`needless_parens_on_range_literals`]

changelog: Adds a new lint [`needless_parens_on_range_literals`] to warn on needless braces on literals in a range statement

For example, the lint would catch

```log
error: needless parenthesis on range literals can be removed
  --> $DIR/needless_parens_on_range_literals.rs:8:13
   |
LL |     let _ = ('a')..=('z');
   |             ^^^^^ help: try: `'a'`
   |
   = note: `-D clippy::needless-parens-on-range-literals` implied by `-D warnings`
```