Fix code quality issues from V4 changes

This https://github.com/topcoder-platform/topcoder-react-lib/pull/30 PR introduced code quality issues that should be fixed.

Most of them are in https://github.com/topcoder-platform/topcoder-react-lib/blob/1e4b154636c86c111b964c0258e6a6706735cf1a/src/services/challenges.js but everything should be checked and fixed.

• [x] Fix eslint issues and revert rules to the default configs
• [x] Fix many typos v3 => v4 in method documentation.
• [x] We use the getApiResponsePayloadV3() method with the response from the V4.
• [x] getApiV3 is defined but never used.
• [x] We defined both this.private.api and this.private.apiV4 as getApiV4(tokenV3). This is confusing.

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