Remove legacy methods of ci pipeline

What does this MR do?

This is the second iteration of removing legacy pipeline processing: #218536 (closed)

In this MR, we are removing Ci::Pipeline#update_legacy_status and Ci::Pipeline#latest_builds_status methods.

suggestion: !37339 (comment 391423105)

❗ This branch is based on !37339 (merged) because that is not merged yet.

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
• 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