refactor clearing HDD cache to remove empty directories

[stklcode]

Initially discussed in PR #286 and reported by @raffaelj

My main concern was to delete the empty folder after invalidating the page cache.
[...]
I think, it would be better to add an additional check, if the folder is empty. If so, the empty folder should be deleted by default - regardless of the $recursive = false option.

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Proposed solution:

We opt out early, if a directory was already empty before and delete emptied directories only in recursive mode.

Remove the early return and the additional condition, so we do not leave behind empty directories.

[sonarcloud]

Quality Gate passed

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