Remove heading from Feature Flags section

What does this MR do?

The heading on the Feature Flags section is removed so not to break the layout following the proposal.

Additional

Removing the title requires the navigation tabs not to be rendered conditionally anymore as it would make the right-side controls look jumpy:

jumpy	not jumpy
jumpy-nav	not-jumpy-nav

Issue: #9231 (closed)

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