Auto merge of #5599 - dtolnay:letif, r=flip1995

Downgrade useless_let_if_seq to nursery

I feel that this lint has the wrong balance of incorrect suggestions for a default-enabled lint.

The immediate code I faced was something like:

```rust
fn main() {
    let mut good = do1();
    if !do2() {
        good = false;
    }
    if good {
        println!("good");
    }
}

fn do1() -> bool { println!("1"); false }
fn do2() -> bool { println!("2"); false }
```

On this code Clippy calls it unidiomatic and suggests the following diff, which has different behavior in a way that I don't necessarily want.

```diff
- let mut good = do1();
- if !do2() {
-     good = false;
- }
+ let good = if !do2() {
+     false
+ } else {
+     do1()
+ };
```

On exploring issues filed about this lint, I have found that other users have also struggled with inappropriate suggestions (https://github.com/rust-lang/rust-clippy/issues/4124, https://github.com/rust-lang/rust-clippy/issues/3043, https://github.com/rust-lang/rust-clippy/issues/2918, https://github.com/rust-lang/rust-clippy/issues/2176) and suggestions that make the code worse (https://github.com/rust-lang/rust-clippy/issues/3769, https://github.com/rust-lang/rust-clippy/issues/2749). Overall I believe that this lint is still at nursery quality for now and should not be enabled.

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changelog: Remove useless_let_if_seq from default set of enabled lints

0 files changed, 0 insertions, 0 deletions