ovl: remove unneeded ioctls

The FS_IOC_[GS]ETFLAGS/FS_IOC_FS[GS]ETXATTR ioctls are now handled via the
fileattr api.  The only unconverted filesystem remaining is CIFS and it is
not allowed to be overlayed due to case insensitive filenames.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>