Use the `all` matcher to check the existence of each path.

This change allows us to remove the `RSpec/IteratedExpectation` rule from `.rubocop_todo.yml` as we no longer iterate over each path to check existence.

Note: We this PR didn't change the subsequent test checking for the negative expectations as this isn't part of the rule (see: https://github.com/rubocop-hq/rubocop-rspec/issues/278).