mtd: kill old field for `struct mtd_info_user'

The ecctype and eccsize fields have been obsolete for a while. Since they
don't have any users, we can kill them and leave padding in their place
for now.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>