Update billing page trial CTAs

What does this MR do?

Does two fixes for both group billing page and the personal billing page.

• Removes the top trial banner from both the group and personal billing pages
• The Gold trial CTA on both the group billing page and the personal billing page should direct users into the new trial signup flow. https://gitlab.com/-/trial_registrations/new

Issue #36747 (closed)

Screenshots

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

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