refactor: remove isPrivate (#61952)

client/utils/build-challenges.js

@@ -45,7 +45,6 @@ exports.buildChallenges = async function buildChallenges() {
     }, []);
 
   const builtChallenges = blocks
-    .filter(block => !block.isPrivate)
     .map(({ challenges }) => challenges)
     .reduce((accu, current) => accu.concat(current), []);
   return builtChallenges;

client/utils/gatsby/challenge-page-creator.js

@@ -102,8 +102,6 @@ exports.createChallengePages = function (
       id,
       isLastChallengeInBlock
     } = node.challenge;
-    // TODO: challengeType === 7 and isPrivate are the same, right? If so, we
-    // should remove one of them.
 
     createPage({
       path: slug,