Draft: Remove welcome message on dashboard

What does this MR do?

Removes the welcome message on the dashboard when the user has no projects or groups yet.

• We recently introduced the "Welcome page" which welcomes the user during sign up
• We additionally have a "Welcome! You successfully signed up" message

Why?

This screen can get overwhelming already for new users, see screenshots. Let's try to reduce this.

Screenshots

Before with all banners	After with all banners	After without any banner

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