xfs: fix online repair block reaping

These patches fix a few problems that I noticed in the code that deals
with old btree blocks after a successful repair. First, we clarify how
the reaping function works w.r.t. bitmap lifetimes.  Next we fix a bug
where we could incorrectly invalidate old btree blocks if they were
crosslinked.  Finally, we convert the reap function to use EFIs so that
we can delete blocks without overloading a transaction.
-----BEGIN PGP SIGNATURE-----
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=aw3l
-----END PGP SIGNATURE-----