Releases file handles when deleting storage groups

Currently, all data is deleted after the "delete storage group root.*" command is successfully executed on the client. That is, no data exists when the "show storage group" or "select * from root" command is executed. However, disk space usage does not decrease.

If lsof -p:pid is used,we can see that the handle of files are not released, causing the operating system to fail to delete the file.

After the IoTDB process is killed, the disk space usage returns to 0.