Remove learn gitlab popover

What does this MR do?

Part of the default to onboarding issue board cleanup.

Context: The Onboarding Issues Experiment creates a learn-gitlab project with issues for the user to start their gitlab journey. We now redirect directly to this issue board after the signup flow got completed with !52520 (merged). Therefore, we no longer need to show a popover to direct the user to go to the issue board.

No changelog because it's still behind a feature flag of the onboarding issue experiment.

How to replicate

• Feature.enable_percentage_of_time(:onboarding_issues_experiment_percentage, 100)
• Signup with a new user and go through all steps
• You should end up at the issue board of the learn-gitlab project and no longer see the popover in the group overview page or in the project page

Screenshots of removed popover (strongly suggested)

Popovers that got REMOVED

1st Popover (group overview)	2nd Popover (project overview)	2nd Popover (in project issues page)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team