Remove backward compatibility code

What does this MR do?

This MR removes backward compatibility code that was added with the updated code in 12.2. We are now developing for 12.7. The jobs run quickly enough that it is very unlikely that any of these jobs will remain by the time an installation is running 12.7.

Those who didn't wait for the affected jobs to run before upgrading from 12.1 to 12.7 may need to click "Reverify all repositories" again afterward.

Closes #13318 (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.

Closes #13318 (closed)