Fix: offline file deletion issue

[IvanStepanok]

The previous implementation only deleted individual files (like index.html) instead of the entire folder containing offline lesson content. This update replaces fileUrl(for:) with fileOrFolderUrl(for:) in deleteFile() and deleteAllFiles() methods, ensuring that both files and folders are handled correctly. The new method dynamically checks the content type and deletes the appropriate folder or file.

[openedx-webhooks]

Thanks for the pull request, @IvanStepanok!

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[volodymyr-chekyrta]

LGTM