Remove unused method matcher for pending steps without reason

[ydah]

Before:

❯ find . -type f | xargs grep "pending_step_without_reason"
./lib/rubocop/cop/rspec/pending_without_reason.rb:        # @!method pending_step_without_reason?(node)
./lib/rubocop/cop/rspec/pending_without_reason.rb:        def_node_matcher :pending_step_without_reason?, <<~PATTERN

After:

❯ find . -type f | xargs grep "pending_step_without_reason"

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• [-] Added tests.
• [-] Updated documentation.
• [-] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[pirj]

Thank you!