Undeleted temporary files

Step #2 of views_data_export_garbage_collect() function should indeed take care of deleting the temporary files. However, in cases where that delete fails for whatever reason, the file_usage entry is not removed from the database, but the views_data_export entry is. The file_delete() only removes the file_usage if the actual file delete was successful, even when the force parameter is true. The attached patch explicitly removes the file_usage before doing the delete. This will allow system_cron to attempt to delete the stuck expired temporary file without logging an error that it is in use by views_data_export. Additionally, make sure that views_data_export_cron runs prior to system_cron so this garbage collect happens before system_cron.

Version of the patch for PHP 7