Revert "fix(case-studies): map _caseStudy field to first title (#234)"

This reverts commit ab87eaa.

Author: Vasyl Yaremchuk

website/modules/testimonials/index.js

@@ -106,10 +106,6 @@ module.exports = {
         label: 'Organization',
         name: 'organization',
       },
-      _caseStudy: {
-        label: 'Related Case Study',
-        name: '_caseStudy.0.title',
-      },
     },
   },
   filters: {