Any way to delete custom fields of cards in Contacts.app?

Some custom fields of contact cards in Contacts.app are really annoying. For example, nicknames always appear in Mail.app. To make things worse, there seems to be no menu option to delete custom fields from cards once created.

Is there any way to delete custom fileds from cards? For example, with an AppleScript? I tried to write one but failed.

Oh, another thing is prefixes. I used to add Mr., Ms., Dr., Prof. etc. to distinguish but they turned out to be really superfluous and silly.