Remove a case that is not negative examples in the capybara sheet

[ydah]

!expect(page).to have_button('Save')

The above case is a new Bad case added by https://github.com/rstacruz/cheatsheets/pull/1798 . It is designated as Bad due to performance issues, but it is not actually a Negative example. In practice, the following would be the same test:

expect(page).to have_button('Save')
!expect(page).to have_button('Save')

This is not an example that will appear on the capybara cheat sheet, because it is a problem with how RSpec is written. I think it should be removed because it creates confusion.

[rstacruz]

Good call, thanks for this!