Updated the Pronoun enum to remove the unused possessive, and changed it so that "it" pronouns display as "it/its" instead of "it/it".

While technically the object form is "it", we are only using this to render pronouns from PronounDB, which itself renders them as "it/its", matching common usage. Therefore I chose to not overcomplicate the code by adding a second type of override for this, instead I just added a comment about this in case somehow the enum gets used for other things where the distinction is important in the future.