crush: update choose_args on bucket removal

crush: update choose_args on bucket removal

The specific bug I see is that a bucket no longer exists but its
choose_args still does.  However, I'm also taking the opportunity to
verify that the choose_args agrees with the bucket sizes and position
counts everywhere else, too.  Check for

- ids or weight_sets for buckets that don't exist or aren't straw2
- weight_set_positions that don't match the choose_args
  - don't fix this, just warn.  i'm not sure how it would happen.  :/
- weight_set sizes that don't match the bucket size

Fixes: http://tracker.ceph.com/issues/24167
Signed-off-by: Sage Weil <sage@redhat.com>