Remove reviewer step and update CE/EE reviewers

Being a CE/EE reviewer is already the default for all engineers, according to the onboarding template:

https://gitlab.com/gitlab-com/people-ops/employment/blob/master/.gitlab/issue_templates/onboarding.md#for-engineering-such-as-developers-build-infrastructure-etc-only

New Team Member: Ensure that you've added yourself as a reviewer for gitlab-ce and gitlab-ee. You can do this by adding the appropriate entries to the data/team.yml with which you added yourself to the team page.