Twitter Card Options is hardly coded and integrate into Open Graph Option. If removed it may can not work propery or cause errors.
Also Twitter Card Summary is using as “Default Card, including a title, description, thumbnail, and Twitter account attribution” for a website which is default & following the rules provided by twitter.
Mostly the important part is, this <meta name=”twitter:card” content=”summary” /> tags is needed & searched by twitter card validator when the website goes for validate.
You can check here for the brief details https://dev.twitter.com/cards/types/summary
