Remove discovery examples documented in Pajamas from Product Principles

To suggest a change to the Product Handbook, please review the updating the Product Handbook section.

Related to:

Overhaul the core navigation experience (gitlab-org&9044)
↳ Pajamas documentation updates based on navigati... (gitlab-org/gitlab-services/design.gitlab.com#1501 - closed)

Please provide a brief explanation for this change:

The examples listed are duplicative and can sometimes conflict with Pajamas on guidance in some cases. In order to support a single source of truth for design patterns, these examples have been removed.

Examples:

• Empty state use cases are documented in Pajamas.
• Banner guidelines are documented in Pajamas
• Alerts guidelines are documented in Pajamas
• Navigation is defined in Pajamas but there are a few conflicting things to note
  • "Leveraging navigation is an effective design paradigm to introduce a user to a new feature or area of GitLab." Pajamas specifically discourages this "We do not add new top-level menu items in order to: Improve discoverability of new features."
  • The "hotspot" component or pulsing blue dot feature has not been solidified in Pajamas yet, so it should not be encouraged under Navigation for feature discoverability. See gitlab-org/gitlab-services/design.gitlab.com#535 for progress.

Please indicate the types of revisions being suggested for the Product Handbook (please check all that apply):

• Small improvement (typos, clarifications, etc.)
• Adding a new section
• Modifying existing section
• Documenting a new process
• Adding a new page or directory
• Other - Removal

Please indicate Milestone

• Assigned to Milestone

Author Checklist

• Provided a concise title for the MR
• Provided a brief explanation for this change (Say why, not just what)
  • (Attach screenshots, Slack conversations, etc. as necessary)
• Indicated the types of changes included in this MR
• Verified that no confidential data is in this MR
• Assigned reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #product or #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.