Deprecate API v2 (#7761)

* deprecate api-v2

* remove v2 test helpers

* remove unused string

test/api/v2/challenges/GET-challenges_id.test.js

@@ -1,34 +0,0 @@
-import {
-  createAndPopulateGroup,
-  generateChallenge,
-} from '../../../helpers/api-integration/v2';
-
-describe('GET /challenges/:id', () => {
-  context('Member of a challenge', () => {
-    let leader, party, challenge;
-
-    before(async () => {
-      let {
-        group,
-        groupLeader,
-      } = await createAndPopulateGroup();
-
-      party = group;
-      leader =  groupLeader;
-      challenge = await generateChallenge(leader, party, {
-        name: 'a created challenge',
-        shortName: 'aCreatedChallenge',
-        description: 'a description for the challenge',
-      });
-    });
-
-    it('returns the challenge object', async () => {
-      let fetchedChallenge = await leader.get(`/challenges/${challenge._id}`);
-
-      expect(fetchedChallenge.name).to.eql(challenge.name);
-      expect(fetchedChallenge.shortName).to.eql(challenge.shortName);
-      expect(fetchedChallenge.description).to.eql(challenge.description);
-      expect(fetchedChallenge.members).to.have.a.lengthOf(1);
-    });
-  });
-});