Remove duplicated sidebar toggle when signed out

What does this MR do?

The right sidebar toggle button is showing up duplicated when the user is signed out.

This MR restores the original logic, even though it isn't great to begin with:

• If signed in: toggle is displayed on ToDos
• If signed out, ToDos don't show: toggle is displayed on the Assignees

Never on reviewers, but it was included when we duplicated the code.

Screenshots (strongly suggested)

When	Before	After
Signed out
Signed in

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

Addresses #296658 (closed)