Removes outdated content from pajamas docs within UX handbook and links to lifecycle docs

Why is this change being made?

Docs were outdated and parts were redundant with the new lifecycle docs. Relevant content that was removed was moved to gitlab-org/gitlab-services/design.gitlab.com!1638 (merged).

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what