Remove unnecessary clone from needless_collect example

[mickvangelderen]

The example for clippy::needless_collect is written as follows:

let len = iterator.clone().collect::<Vec<_>>().len();
// should be
let len = iterator.count();

With this change, the unnecessary clone() is removed and the the standard

### Example
```rust
// original
```
Use instead:
```rust
// improved
```

structure is followed.

Discussion: #10784 (comment)

changelog: [needless_collect]: Cleaned up the example in the lint documentation.

[rustbot]

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[Alexendoo]

Thanks!

@bors r+

[bors]

📌 Commit 79eb06c has been approved by Alexendoo

It is now in the queue for this repository.

[bors]

⌛ Testing commit 79eb06c with merge 9cd483d...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Alexendoo
Pushing 9cd483d to master...