Documentation fixes

[ageorgou]

• In the page describing the lints, the View Source links are incorrect. This PR removes the extra segment causing them to fail.
  • Example before: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/clippy_lints/src/absolute_paths.rs#L13
  • Example after: https://github.com/rust-lang/rust-clippy/blob/master/clippy_lints/src/absolute_paths.rs#L13
  • I think this was introduced in Rewrite lints page #13269.
  • I've only checked a few of the lints with the new template, but from what I can tell the metadata is generated in the same way for all of them. The id_location contains the full path of the lint declaration in the repository, which is why clippy_lints was repeated in the URL.
• Separately, fixing a typo in the explanation of unnecessary_get_then_check.

changelog: none

[rustbot]

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[xFrednet]

Welcome to Clippy, and thank you for the update! :D

These changes look good to me, nice catch with the URL!

---

Roses are red,
Violets are blue,
this contains keys,
and correct URLs

[bors]

📌 Commit 4863625 has been approved by xFrednet

It is now in the queue for this repository.

[bors]

⌛ Testing commit 4863625 with merge ccb30bf...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing ccb30bf to master...