LPS-34437 Fix Preview and Thumbnail delete on importing LAR file

Hi Tibi,

You probably know this issue, I had e-mail conversations with Tina and Sergio, and 
```
DLStoreUtil.deleteDirectory(companyId, REPOSITORY_ID, dirName);
```
was accepted as the solution. I've just send it to you as I have some additional changes to extract the directory from the file's path, so perhaps you can still point out something before sending it forward.

Regards,
Vilmos