linux-wandboard

md: remove some dead fields from mddev_s

These fields have never been used.
commit 4b6d287f627b5fb6a49f78f9e81649ff98c62bb7
added them, but also added identical files to bitmap_super_s,
and only used the latter.

So remove these unused fields.

Signed-off-by: NeilBrown <neilb@suse.de>