[PATCH] md/bitmap: remove dead code from md/bitmap

bitmap_active is never called, and the BITMAP_ACTIVE flag is never users or
tested, so discard them both.

Also remove some out-of-date 'todo' comments.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>