reset experiment

[SabrinaTardio]

Task/Issue URL: https://app.asana.com/0/1204186595873227/1209311973888722

Description: Restart onboarding experiment with contextual onboarding

Optional E2E tests:

• Run PIR E2E tests
  Check this to run the Personal Information Removal end to end tests. If updating CCF, or any PIR related code, tick this.

Steps to test this PR:

1. Run ./clean-app.sh debug
2. In Tab.swift in shouldShowOnboarding returns comment out everything besides lines 94 and 95
3. Run the app and should get one of the two onboardings
4. Check the m_mac_onboarding_cohort-assigned pixel is sent with the right cohort (oh for the old and og for the new)
5. Check that at the end of the old onboarding there is no contextual onboarding
6. Check that at the end of the new onboarding there is the contextual onboarding

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• Does this PR satisfy our Definition of Done?

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[alessandroboron]

Tested and works as expected! Instructions for cohort variants were flipped but I checked the code and it’s all good!