Remove several performance cops

[koic]

Follow up rubocop/rubocop#6870 and rubocop/rubocop@32ed7d1.

The commits are independent according to upstream (rubocop-hq/rubocop) so that we can revert individually and when necessary.

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[Drenmi]

🚀