style: include `unnecessary_join`

[vil02]

Pull Request Template

Description

This PR removes the unnecessary_join from the list of suppressed lints.

Continuation of #743.

Checklist:

• [x] I ran bellow commands using the latest version of rust nightly.
• [x] I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• [x] I ran cargo fmt just before my last commit.
• [x] I ran cargo test just before my last commit and all tests passed.
• [x] I added my algorithm to the corresponding mod.rs file within its own folder, and in any parent folder(s).
• [x] I added my algorithm to DIRECTORY.md with the correct link.
• [x] I checked COUNTRIBUTING.md and my code follows its guidelines.

Please make sure that if there is a test that takes too long to run ( > 300ms), you #[ignore] that or try to optimize your code or make the test easier to run. We have this rule because we have hundreds of tests to run; If each one of them took 300ms, we would have to wait for a long time.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.02%. Comparing base (08ce80c) to head (460c277). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #752 +/- ## ========================================== - Coverage 95.02% 95.02% -0.01% ========================================== Files 304 304 Lines 22599 22595 -4 ========================================== - Hits 21475 21471 -4 Misses 1124 1124 ```

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