xfce46: remove checksum name atribute from bbclass

xfce46: remove checksum name atribute from bbclass

* ie xfce-base/libxfce4util_4.6.1.bb cannot find it's checksums anymore
* commit e3df76459f7710af61d1b51066e0685c822dbe7b introduced
  name=archive in xfce46.bbclass without adding archive name to all
  recipes using xfce46
* I agree that in case someone will need additional SRC_URI item in
  recipe inheriting xfce46 he will have to add it to this bbclass AND
  update all recipes using it.
* Feel free to fix it the other way around if you expect more
  SRC_URIs/recipe.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>