Stop using UrlHelper includes in specs

What does this MR do and why?

Closes #341401 (closed)

And thus completes the work on &6767 (closed)

---

The following, yq-based script can reproduce the changes:

todos='.rubocop_todo/rails/include_url_helper.yml'
files=$(yq '."Rails/IncludeUrlHelper".Exclude.[]' < $todos)

for file in $files; do

  # Remove todo
  sd "\- $file" '' $todos

  # Remove include & correct resulting violation
  sd 'include ActionView::Helpers::UrlHelper' '' "$file"
  bundle exec rubocop --auto-correct "$file"

  # Update known helper method calls
  sd ' link_to' ' ActionController::Base.helpers.link_to' "$file"
  sd ' mail_to' ' ActionController::Base.helpers.mail_to' "$file"
  bundle exec rspec "$file"
done

rm $todos

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