Delete deprecated Resource-related methods in ClasspathScanner

[marcphilipp]

Second step to fully resolve the package cycle (see #4885) for 6.0 that should not be backported to the 5.x line.

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Definition of Done

• There are no TODOs left in the code
• Method preconditions are checked and documented in the method's Javadoc
• Coding conventions (e.g. for logging) have been followed
• Change is covered by automated tests including corner cases, errors, and exception handling
• Public API has Javadoc and @API annotations
• Change is documented in the User Guide and Release Notes

[marcphilipp]

We've decided to defer deleting the deprecated code until 6.2 to allow for a better upgrade experience.

Closing in favor of

• Delete code that was deprecated in 5.14 or earlier #4940