[selectors] Repeated "same as :first-child:last-child" #1308
Description
Commit be7492c added a sentence to :only-child, but I think this was an unintended mistake, because the same sentence was already just below there.
The :only-child pseudo-class represents an element that has no siblings, same as :first-child:last-child. Same as :first-child:last-child or :nth-child(1):nth-last-child(1), but with a lower specificity.