Fix/redirect issues

[ideadude]

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• [x] Have you followed the Contributing guideline?
• [x] Does your code follow the WordPress' coding standards?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

We had 2 different functions redirecting away from BP and/or to/from the PMPro Levels page. There were lots of edge cases we had code for. This update cleans up those functions to make it more clear what's happening in the code.

Andrew will test to make sure all the previously accounted for edge cases are still handled properly.

Other information:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [x] Have you successfully run tests with your changes locally?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

[andrewlimaza]

I ran various tests with various settings of the registration page. It works well and doesn't cause any loops anymore. Code is so much neater, thanks!