CopyDocument with overwrite existing does not overwrite existing translations, making a failed partial copy

When copying a document with translation over another existing document with translation, using XWiki#copyDocument() with force parameter set to true, the original document is overwritten, but translation are not, and the copy return false.

This is due to the XWiki#deleteDocument() method used to delete the target document prior to the copy when the force is in action. This delete method does not take care of translation, so only the original document is dropped. This might reveal a larger bug regarding document deletion.