staging: exfat: remove DOSNAMEs.

remove 'dos_name','short_name' and related definitions.

'dos_name' and 'short_name' are definitions before VFAT.
These are never used in exFAT.

Signed-off-by: Tetsuhiro Kohada <Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp>
Link: https://lore.kernel.org/r/20200217072941.34116-1-Kohada.Tetsuhiro@dc.MitsubishiElectric.co.jp


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>