Remove legacy container image checking from Project container top

What does this MR do?

Removes the legacy container image checking mechanism from Project Container Registry top page.

Initially gitlab-foss!10109 (merged) introduced the private method removing in the MR (%9.1), but !27814 (merged) completely removed the request to that endpoint we are removing.

The importance and disadvantage of that mechanism was discussed at gitlab-foss!10109 (comment 27209318) in 2017.

The removal of the method would reduce the requests of both container registry and database.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content