TYPO3 Core

1. Even if we add a check around it, it's most probably set.
   twitter_card is a select field with the options summary and summary_large and the default of summary.
   So if nothing is changed, the value will be summary, the condition will become true and the meta tag gets rendered.
2. twitter:card is still the valid and official meta tag, according to the X Developer Platform (see: https://developer.twitter.com/en/docs/twitter-for-websites/cards/guides/getting-started#started)
3. AFAIK twitter assumes summary if nothing is set, so it wouldn't make a difference to remove it.

What is the specific use case for which you want to remove the meta tag? Maybe this will help to understand the requirement better and offer a solution.