sftpfs: improve remove

we know if the client asks to remove a file or directory so let's
use the appropriate command without letting the sftp library guess
the appropriate behavior

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

vfs/sftpfs.go

@@ -335,6 +335,9 @@ func (fs *SFTPFs) Remove(name string, isDir bool) error {
 	if err := fs.checkConnection(); err != nil {
 		return err
 	}
+	if isDir {
+		return fs.sftpClient.RemoveDirectory(name)
+	}
 	return fs.sftpClient.Remove(name)
 }