Remove old storage compatibility classes

What does this MR do?

In #299853 (closed), we moved several classes and workers to a different namespace, in order to align the codebase and have every class scoped.

In 14.0 we can remove those classes since all workers should have finished before updating to 14.0 because we couldn't before according to our guidelines.

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Related to #322393 (closed)